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3 Firearms Identification and the â Use of Ballistics Evidence This chapter provides a key context for the next part of the report by examining the nature of ballistics evidence itself and the ways it has been analyzed and used over the past century. Since the primary focus in this study is the ability of computer-based systems to discern unique charac- teristics in ballistics evidence on the basis of images of different sorts, it is useful to first consider how uniqueness and reproducibility of characteristic marks have been discerned through the particular media of the comparison microscope and the human eye. We briefly describe the general nature of toolmarks as evidence (Sec- tionÂ 3âA) and then outline the basic history and theory of firearms iden- tification (3âB). Section 3âC summarizes the literature on the uniqueness, reproducibility, and permanence of marks as detected by traditional meth- odology. The circumstances of firing a weapon, the manufacture of firearms and ammunition, and measures taken (or not taken) by firearms users can all pose various complications to the identification and linking of ballistics evidence; we review some of these issues in Section 3âD. Section 3âE offers key commentary on the scope of the committeeâs work in the context of the material in this chapter. The final section (3âF) briefly describes the general role of imaging and photography in firearms identification, as a prelude to the next section of the report. 3âAâ Toolmarks as Evidence Various branches of forensic scienceâdealing with the analysis of evi- dence as diverse as handwriting samples and soil or mineral samplesâare 53
54 BALLISTIC IMAGING increasingly compared with one of their sister branches: the analysis of deoxyribonucleic acid (DNA) markers and identification based on those markers. As we note in Section 1âC, the term âballistic fingerprintingâ has also come into common (albeit somewhat inaccurate) usage to describe some features of firearms identification, suggesting a comparison with fingerÂprint evidence. Firearms toolmark evidence differs from DNA and fingerprint evidence due to their basic point of reference: the former links to a particular firearm while the latter two link to a particular person. Links between pieces of bal- listics evidence can point to a common gun from which exhibits were fired, but not necessarily to the same person pulling the trigger. A potential match suggested by a national reference ballistic image database could suggest a link from a piece of crime scene evidence to an original firearm point of sale, but that link is at least doubly indirect: the link is only to the location of the transaction and not immediately to the firearmâs purchaser, and sub- sequent identification of the purchaser does not necessarily mean that the purchaser still possesses the gun (or fired the shot in a crime). However, it is important to consider thatâalone, absent any other evidence or knowl- edge of circumstancesâeven person-specific fingerprint and DNA evidence is necessarily one step removed and indirect. It is possible for fingerprint or DNA evidence to be present and retrievable at crime scenes without its source person having been the crimeâs perpetrator. Forensic evidence can be usedâin combination with other investigative findingsâto develop a theory of what transpired at the scene and who may have committed the crime, but the link to any specific person from the ballistics evidence alone is necessarily indirect. Toolmark evidence and DNA evidence are markedly different in another crucial respect, which is the subjectivity inherent in the analysis. Firearms identification ultimately comes down to a subjective assessmentâspecifi- cally, a subjective probability statement (although practitioners often render these as absolute statements). Firearms examiners observe concrete, objec- tive phenomena, butâas Thornton and Peterson (2002:24â25) observe, âthere is an incredible amount of difficulty attached to the development of a statistical basis for evidence evaluationâ in forensic science fields like firearms examination: Behind every opinion rendered by a forensic scientist there is a statistical basis. We may not know what that basis is, and we may have no feasible means of developing an understanding of that basis, but it is futile to deny that one exists. . . . The most common and coherent theory of forensic identification is that where there is a high degree of variation among a Â ttributes (of toolmark striations, writing, friction ridges on skin, and so on), then where a âmatchâ is observed the probability that the match is
FIREARMS IDENTIFICATION 55 coincidental rather than reflecting a shared source will be very small. . . . Forensic individualization sciences that lack actual data, which is most of them, have no choice but to either intuitively estimate those underlying probabilities and calculate the coincidental match probability from those subjective probabilities, or simply to assume the conclusion of a miniscule probability of a coincidental match (and in fact they do the latter). In the specific context of firearms and toolmark examination, derivation of an objective, statistical basis for rendering decisions is hampered by the fundamentally random nature of parts of the firing process. The exact same conditionsâof ammunition, of wear and cleanliness of firearms parts, of burning of propellant particles and the resulting gas pressure, and so forthâ do not necessarily apply for every shot from the same gun. Ultimately, as firearms identification is currently practiced, an examinerâs assessment of the quality and quantity of resulting toolmarks and the decision of what does or does not constitute a match comes down to a subjective determination based on intuition and experience. By comparison, DNA analysis is practically unique among forensic science specialties as having a strong objective basis for determination and as being amenable to formal probability statements. Thornton and Peterson (2002:Fig. 1) rank various forensic science sub- fields on a continuum of relative subjectivity. On the low end of that scale is DNA analysis, along with serology (blood type determination) and drug and narcotic identification. They identify firearms and toolmark identifica- tion as having relatively high subjectivity, on par with fiber identification. They identify blood spatter interpretation, voiceprint analysis, and bite- marks as a group of forensic science specialties just slightly more subjective than toolmark identification, and handwriting and hair identification as a cluster slightly more subjective yet. 3âBâ Traditional Firearms Identification Smith (2004:130) succinctly summarized the basic task of a firearms examiner in making an identification between pieces of evidence: Before a microscopic comparison begins, a foundation is built by measur- ing and comparing available class characteristics, such as General Rifling Characteristics (GRCs). These objective criteria are used to narrow the pool of candidates for determining a common source. Once an available foundation has been established, a common source often can be deter- mined by evaluating individual microscopic marks of value using pattern recognition. In traditional firearms identificationâpart science and part art form, still carried out today using the same basic tools that gave rise to the field
56 BALLISTIC IMAGING in the 1930sâthe firearms examiner faces the formidable cognitive task of forming a mental pattern of identifying marks and features on bullet and cartridge case evidence. That pattern must then be matched to those from other exhibits. 3âB.1â Individualization and Identification: Class, Subclass, and Individual Characteristics The label âfirearms identificationâ is another instance in which lan- guage can be a bit elusive. Although âthe terms âidentificationâ and âiden- tityâ are used constantly by practitionersâ of criminalistics, or the forensic analysis of evidence, Kirk (1963:236) argued that the usage is an âunfor- tunate failure of nomenclature.â Rather than identification (as that term is commonly understood), Kirk argues that âcriminalistics is the science of individualization:â The criminalist does not attempt identification except as a prelude to his real functionâthat of individualizing. The real aim of all forensic science is to establish individuality, or to approach it as closely as the present state of the science allows. . . . What was actually done was not the identification of the fingerprint, but rather the individualization of a person as the one who left the fingerprint. . . . [Likewise,] if the firearms examiner said that the bullet was a Colt 45 A.C.P. but could not individualize the gun that fired it, his value would be relatively slight. Thornton and Peterson (2002:8, 9) further differentiate between the two terms: âIndividualization is the process of placing an object in a unit category which consists of a single unit. Individualization implies unique- ness; identification, strictly speaking, does not require it.â They also note the frequent use in forensic science of âidentificationâ when âindividual- izationâ is meant, but recognized that âit is a constraint imposed by our languageâ; relying on the term âindividualizeâ would likely lead to public confusion. âIt should be appreciated, however, that the process of identi- fication means one thing to the forensic scientist, and another thing to the botanist or the zoologist.â (See also Champod [2000:1077] on âindividu- alizationâ versus âidentification.â) The phrasing of âindividualizationâ as the act of associating an object â urther F information on current practice in firearms identification and images connected with that work are available through resources at the Association of Firearm and Tool Mark Examiners (http://www.afte.org) and the Scientific Working Group for Firearms and Tool- marks (http://www.swggun.org). Additional information and imagesâand tools for simulat- ing the use of the comparison microscope for comparing bullet and cartridge evidenceâare accessible at http://www.firearmsid.com.
FIREARMS IDENTIFICATION 57 with a category that contains only one unit is a useful one in addressing the basic approach of firearms examination. Firearms examiners typically give testimony to the effect that this particular gun, and not any other gun in the world, was used to fire particular shots. Yet even in the professionâs earliest days, Hatcher (1935:266) anticipated a common reply to this type of argument: The firearms witness may expect to be asked how he can be sure of his findings, in view of the fact that he can have examined only a few of the countless thousands of guns that exist. But how does [an eyewitness to the crime] that identified the prisoner know that some other person may not look exactly like him? He will say that he has seen enough people in his life to know that the rule is that all people look different, and that the chances are overwhelmingly against finding two people who look so much alike that they cannot be told apart. In precisely the same way, the firearms expert, who admittedly cannot have actually examined more than the tiniest fraction of a percent of all the guns in the world, can still have had enough experience to be well aware of what differences do occur, and to know that the chance of finding two bullets from different guns that are exactly alike in every detail of their surface markings is infinitesimally small. The same thing applies with equal force to the finger-print method of identification. Subsequently, he posited this idea more succinctly: âIt may be quite common for two or more prominent individual marks on bullets from two entirely different guns to match exactly, but the chance that there will be a correspondence of a great many of the individual characteristic marks on two bullets that came from different guns is so remote as to amount to a practical impossibilityâ (Hatcher, 1935:288). The basic approach to identification in forensic science developed into the concept of class characteristics and individual characteristics. Thornton and Peterson (2002:5â6) define these concepts: Class characteristics are general characteristics that separate a group of objects from a universe of diverse objects. In a comparison process, class characteristics serve the very useful purpose of screening a large Ânumber of items by eliminating from consideration those items that do not share the characteristics common to all the members of that group. Class characteris- tics do not, and cannot, establish uniqueness. Individual characteristics, on the other hand, are those exceptional characteristics that may establish the uniqueness of an object. It should be recognized that an individual charac- teristic, taken in isolation, might not in itself be unique. The uniqueness of an object may be established by an ensemble of individual characteristics. A scratch on the surface of a bullet, for example, is not a unique event; it is the arrangement of the scratches on the bullet that mark it as unique.
58 BALLISTIC IMAGING In the context of examining bullet and cartridge case evidence, such parameters as caliber and the number of lands and grooves are class char- acteristics that can be used to screen or filter out possible comparisons that could not possibly have been fired from the same gun. Other class char- acteristics include firing pin shape (for instance, the distinctive rectangular firing pin impressions left by Glock firearms) or pronounced âdrag marksâ that can be caused by firing pins as the cartridge case goes through the ejection process. Individual characteristicsâthe fine striations on a bulletâs surface or peculiar microscopic textures in the firing pin impression, for instanceâallow for the set of possible guns from which an exhibit could have been fired to be narrowed. However, a binary split between class and individual characteristics proved too limited to describe the full range of phenomena observed by experienced examiners. In 1985, the Association of Firearm and Tool Mark Examiners (AFTE) convened a committee to develop a consensus document on a theory of toolmark identification and a range of basic conclusions that could be reached from comparison of toolmark evidence. The result, pro- duced in 1989 and unanimously approved by the organizationâs member- ship, is reproduced in Box 3-1. Importantly, the 1989 standard also added a new term to the firearms identification lexicon: subclass characteristics, defined as follows (Moran, 2002:228): Discernable surface features of an object, which are more restrictive than âclass characteristicsâ in that they are â¢ Produced incidental to manufacture â¢ Significant in that they relate to a small group source (a subset of the class to which they belong) â¢ Can arise from a source which changes over time Caution should be exercised in distinguishing subclass characteristics from individual characteristics. As a middle ground between class and individual characteristics, subclass characteristics covered marks or features thatâarising from specific manu- facturing techniques, or flaws in said techniquesâcould induce similar marks on pieces of evidence even though they originated from different â ectangular R firing pin marks were a telltale sign of Glock pistols âprior to the introduction of Smith & Wessonâs Sigma Series, Model SW40F, semi-automatic pistol,â the design of which is very similar to Glock standards. Nichols (1995:133, 134), in documenting the similarity b Â etween this firearmâs marks and the known Glock characteristics, notes that the two highly s Â imilar gun types can be distinguished by ejector and extractor marks, as well as a character- istic âdimple on the [casing] head above the firing pin dragâ on Glock rounds.
FIREARMS IDENTIFICATION 59 BOX 3-1 Association of Firearm and Tool Mark Examiners (AFTE) Theory of Identification and Range of Conclusions Theory of Identification as It Relates to Toolmarks A. The theory of identification as it pertains to the comparison of toolmarks e Â nables opinions of common origin to be made when the unique surface con- tours of two toolmarks are in âsufficient agreement.â B. This âsufficient agreementâ is related to the significant duplication of random toolmarks as evidenced by the correspondence of a pattern or combination of patterns of surface contours. Significance is determined by the compara- tive examination of two or more sets of surface contour patterns comprised of individual peaks, ridges, and furrows. Specifically, the relative height or depth, width, curvature, and spatial relationship of the individual peaks, ridges, and furrows within one set of surface contours are defined as compared to the corresponding features in the second set of surface contours. Agreement is significant when it exceeds the best agreement demonstrated between tool- marks known to have been produced by different tools and is consistent with the agreement demonstrated by toolmarks known to have been produced by the same tool. The statement that âsufficient agreementâ exists between two toolmarks means that the agreement is of a quantity and quality that the likeli- hood another tool could have made the mark is so remote as to be considered a practical impossibility. C. Currently, the interpretation of individualization/identification is subjective in nature, founded on scientific principles and based on the examinerâs training and experience. Range of Conclusions Possible When Comparing Toolmarks The examiner is encouraged to report the objective observations that support the findings of toolmark examinations. The examiner should be conservative when reporting the significance of these observations. The following represents a spectrum of statements: A. IDENTIFICATION: Agreement of a combination of individual characteristics and all discernible class characteristics where the extent of agreement ex- ceeds that which can occur in the comparison of toolmarks made by different tools and is consistent with the agreement demonstrated by toolmarks known to have been produced by the same tool. B. INCONCLUSIVE: a. Some agreement of individual characteristics and all discernible class characteristics, but insufficient for an identification. continued
60 BALLISTIC IMAGING BOX 3-1 Continued b. Agreement of all discernible class characteristics without agreement or disagreement of individual characteristics due to an absence, insufficiency, or lack of reproducibility. c. Agreement of all discernible class characteristics and disagreement of individual characteristics, but insufficient for an elimination. C. ELIMINATION: Significant disagreement of discernible class characteristics and/or individual characteristics. D. UNSUITABLE: Unsuitable for comparison. SOURCES: Excerpted from AFTE Criteria for Identification Committee (1992) and Grzybowski et al. (2003). sources. Two examples of carryover of subclass characteristics are described in Box 3-2. The AFTE theory of identification is rooted in the recognition that âthe interpretation of individualization/identification is subjective in nature.â However, it melds that recognition with more objective, quasi-quantitative benchmarksââsufficient agreement,â âsignificance,â âlikelihood . . . so remote,â and agreement in both âquantity and qualityââbut no specific empirical definition is given for these terms. Importantly, the AFTE theory does set up two cognitive thresholds that must be crossed in order to arrive at the conclusion that two exhibits share the same source, to the exclusion of all others. In describing the comparison of fingerprints, Stoney (1991; quoted in Moran, 2002:233) wrote of the basic cognitive process: When more and more corresponding features are found between two pat- terns, scientists and lay person alike become subjectively certain that the patterns could not possibly be duplicated by chance. What has happened here is somewhat analogous to a leap of faith. It is a jump, an âextrapo- lation,â based on the observation of highly variable traits among a few characteristics, and then considering the case of many characteristics. Duplication is inconceivable to the rational mind and we conclude that there is absolute identity. â he T âleap of faithâ involved in extrapolating to all possible sources in the world was echoed, in specific reference to firearms identification by Rowe (1991). Understandably, some firearms examiners have objected to some overtones of the âleap of faithâ phrasing; for instance, Miller and McLean (1998:17â18) ârespond [to the phrasing] by stating that the published data which does exist, certainly presents enough statistical data to indicate more substance to the identification theory than a âleap of faith.âââ
FIREARMS IDENTIFICATION 61 BOX 3-2 Examples of Subclass Carryover â¢ Lomoro (1974:18) described test firings from F.I.E. Titanic revolvers, in a particular serial number range (but later shown to include some of a different make from the others). These firings produced seemingly similar striation patterns on fired bullets that could be naively matched to each other even though they had been fired from different weapons. âThis pronounced stria [pattern] was only pres- ent on the lands of the bullets and very little if any matching stria was found on the grooves of the bullets. Examination of the bore revealed that either a worn or a very poor rifling tool was used during manufacturing,â causing the similarity be imparted within a batch of separate barrels. â¢ Matty and Johnson (1984) observed that the particular tooling used on some Smith & Wesson firing pins results in a pattern of concentric rings that is re- peatable in consecutively tooled pins. This pattern appears in the firing pin impres- sion, meaning that examiners need to downweight the ring patterns and focus on other individual features to make correct matches on the firing pin impression. He continues that this âleapâ occursâin fingerprinting, as in other branches of forensic science, âwithout any statistical foundation.â In a sense, the AFTE theory of identification requires two extrapola- tions: first, that marks are sufficiently consistent with true matches (pro- duced by the same tool) to have come from the same source, and, second, that the quality and similarity of corresponding features exceed the best known apparent agreement between true nonmatches (produced by differ- ent tools). It follows that both of these extrapolationsâbut particularly the latterârequire considerable experience in comparing exhibits and training in recognizing significant features. 3âB.2â Historical Evolution Some of the major advances in the field of traditional firearms iden- tification are described in Box 3-3. Calvin H. Goddard, a founder of the Bureau of Forensic Ballistics in the New York City Police Department, is typically credited as the âfatherâ of forensic ballistics in the United States; â iasotti B and Murdock (2002:219â220) advocated the addition of the known nonmatch criterion, beginning with their conclusion in 1984 that âexisting research was insufficient to validate the quantitative objective criteria necessary to conclude that a working surface is unique.â The known nonmatch criterion âadded a quantitative dimensionâ to the mix.
62 BALLISTIC IMAGING BOX 3-3 Highlights in the History of Traditional Firearms Identification â¢ 1900: The Buffalo Medical Journal published âThe Missile and the Weaponâ by Albert L. Hall, commenting on his observations that firearms of different mark impart different striated marks and impressions on fired bullets. â¢ 1907: Cartridge case evidence was examined as part of the investigation of the 1906 Brownsville, Texas, riots in which black soldiers allegedly fired upon a white crowd in retaliation against racial slurs. Thirty-nine cartridges were recov- ered; all but six were matched to four rifles, based on examination of enlarged photographs of firing pin impressions. [Examiners concluded that no identifications could be made on the basis of recovered bullet evidence.] â¢ 1915: Charlie Stielow, an illiterate farmer in New York state, was convicted and sentenced to death for killing his employer and the employerâs housekeeper, the latter of whom was found dead on the doorstep of Stielowâs nearby home. Stielowâs conviction was due in part to testimony by an examiner who claimed to find nine abnormal scratches on the recovered bullets that corresponded to particular defects in the alleged murder weapon. However, a more careful subse- quent analysis of the evidence by Charles Waite concluded that Stielowâs revolver could not have been the murder weapon; Stielow was pardoned and released from prison. â¢ 1925: Philip Gravelle was credited with the development of the comparison m Â icroscope for side-by-side comparison of ballistics evidence in Calvin ÂGoddardâs article âForensic Ballisticsâ in Army Ordinance. Goddard used the technique in the article, and the comparison microscope technique grew in popularity after the Saturday Evening Postâs two-part âFinger-printing Bulletsâ article in 1926 profiled New York Cityâs Bureau of Forensic Ballistics, which Goddard, Gravelle, and Waite helped found. â¢ 1929: On February 14, six members of George âBugsâ Moranâs North Side gang (and one acquaintance) were brutally killed in a Chicago warehouse by six men impersonating police officers, believed to be operatives of rival Al Caponeâs South Side gang, in what quickly became known as the âSt. Valentineâs Day Mas- sacre.â As part of the investigation, Goddard prepared a detailed examination of recovered bullet and cartridge case evidence, connecting them to two Thompson submachine guns and a 12-gauge shotgun. Â Goddardâconsidered the father of modern firearms examinationâsubsequently left New York City to establish the Scientific Crime Detection Laboratory of Chicago, affiliated with Northwestern University. â¢ 1934â1935: First editions of two seminal texts on firearms examination were published: Gerald Burrardâs The Identification of Firearms and Forensic Bal- listics and Julian Hatcherâs Textbook of Firearms Investigation, Identification and Evidence. â¢ 1958: John Davisâ An Introduction to Tool Marks, Firearms and the Stria- graph argued for the use of the striagraph, an early tool for direct measurement of the surface contours of ballistics evidence. Though the striagraph never advanced beyond the research stage, it was a precursor to the use of imaging and profilom- etry techniques for firearms identification.
FIREARMS IDENTIFICATION 63 BOX 3-3 Continued â¢ 1962: J. Howard Matthews, a retired chemistry professor from the Univer- sity of Wisconsin who became interested in forensic science after being called in to assist on a bombing case, published the two-volume Firearms Identification. â¢ 1969: At a 35-member conference hosted by the Crime Laboratory of the Chicago Police Department, firearms identification practitioners form the AssoÂ ciation of Firearm and Tool Mark Examiners (AFTE). The new associationâs news- letter developed into the AFTE Journal in 1973 and continues as a quarterly, peer-reviewed publication; the international association continues to hold an an- nual Training Seminar. SOURCES: Information from Hamby and Thorpe (1999), Hatcher (1935), and Goddard (1999). the text by Hatcher (1935) is generally considered the text on which the modern field of firearms and toolmark examination is based (Nichols, 2003). The modern field of firearms identification owes much to the develop- ment of the comparison bridge, a system of mirrors or prisms that permits the views from two separate microscopic lenses to appear side by side in the same field of view. The device equipped with this optical bridge, called the comparison microscope, was not designed for analysis of bullet or car- tridge case evidence, nor was it first used in such forensic applications (see, e.g., Thornton, 1978; Goddard, 1980). Even early advocates of forensic firearms analysis cautioned against making too much of the technology at hand, noting that the comparison microscope, on its own, has limitations. Foreshadowing some contemporary claims about the capability of ballistic imaging systems, ÂBurrard (1962:131â132) lamented: The most fantastic claims have been put forward for, and the most r Â idiculous descriptions of, [the comparison microscope] which are enough to suggest that it has magical properties, and that it automatically, and wholly of its own accord, rings a bell or utters some similar warning, when the two cartridge cases under examination exhibit the same [individual markings]. Unhappily there is no foundation for this comforting belief. In the hands of a trained microscopist the comparison microscope can be of great value in determining the identity of fired bullets; but for cartridge cases I have come to the conclusion that a high-class single instrument is preferable. . . . And even for fired bullets the comparison microscope offers
64 BALLISTIC IMAGING difficulties in illumination which are never encountered when using a single instrument, for the illumination of opaque objects such as the surfaces of fired cartridge cases and bullets is a far more difficult problem than the illumination of transparencies, fibres or spermatozoa. Nevertheless, the application of the comparison microscope to firearms evidence analysis led the field of firearms identification to flourish and reinforced the analysis of ballistics evidence as a critical part of criminal investigations. In recent years, as the increased workload of state and local law enforce- ment forensic laboratories has created a shortage of firearms examiners, p Â lacing increased attention on the training and recruitment of Âexaminers. Noting that âthere is no college degree a firearms examiner can pursue to reach true proficiency in firearms identification,â and that theÂ core of training activities consists of âextended on-the-job training,â the Bureau of Alcohol, Tobacco, and Firearms (ATF) established a National Firearm Examiner Academy in 1998. The original plan for the academy was for a â16-week intensive program . . . to train Âcandidates to become apprentice firearms examinersâ and a pairing of apprentice Âexaminers with participat- ing law enforcement agencies Â(Ethridge, 1998:703, 704). 3âB.3â Pattern Matching and âLine Countingâ Traditional firearms examination is, fundamentally, one whose central task is pattern matching. Moran (2002:227) summarizes the approach: Toolmark examiners (and examiners in other comparative evidence dis- ciplines) in the United States approach the interpretation of evidence by employing a combination of their cognitive ability to recognize agreement between patterns that in their âminds eyeâ constitutes an identification or âmatchâ between a questioned pattern or toolmark and toolmark pat- terns produced from known tools. . . . This traditional âpattern matchâ a Â pproach (for a lack of a better term) relies on art (the cognitive ability to recognize agreement of pattern) and science (supporting the uniqueness of tool surfaces as a means to establishing an identification between a questioned toolmark and the tool that produced it). Hayes et al. (2004:139â140) add: âIn traditional pattern recognition methodology, the details used to determine a match include the height, â echnically, âpattern matchingâ in forensic science may further be differentiated into two T categories, pattern fit and pattern transfer. Pattern fit is akin to a jigsaw puzzle, determining whether pieces or fragments of some object were once part of a whole object. Firearms tool- marks follow the pattern transfer form, in which patterns are created by the interaction of more than one object (Biasotti and Murdock, 2002:208).
FIREARMS IDENTIFICATION 65 weight, depth, spatial relationship and consecutiveness of the class and indiÂ vidual characteristics. When viewed as a whole, these components become significant.â Pattern matchingâaided by the dual, side-by-side inspection made possible by the comparison microscopeâhas been the historical norm since the field of firearms identification emerged into prominence in the 1930s. As the AFTE theory of identification indicates (Box 3-1), the standard of identification is âcurrently . . . subjective in nature.â In the late 1950s, two important developments were made in order to provide the field with a more objective and quantitative basis. The first, mentioned in Box 3-2, was the development by Davis (1958) of an instrument he called a âstria- graphâ to quantitatively measure the microscopic markings left by firearms on bullets and cartridge cases. The striagraph made traces of the contours of a bulletâs surface using a stylus to record depth. Though the instrument was never developed commercially, it marked the first attempt to develop an explicit âsignatureâ from pieces of evidence for comparison with each other, foreshadowing the signatures that are the basis of todayâs ballistic imaging systems. A more significant development was a study by Biasotti (1959) that formed the foundation for what is now known as the consecutive matching striations (CMS) approach to identification. Nichols (2003:299) relates that this approach has developed and emerged to the point that a âfray appears to have developed within the discipline,â pitting âthe old school tradition of âpattern matchingâ versus the new school of âline counters.ââ Biasottiâs (1959:34) work was motivated by what he described as âan almost complete lack of factual and statistical data pertaining to the prob- lem of establishing identity in the field of firearms identification.â Accord- ingly, he sought to âconduct a direct statistical count of the elements which actually form the basis of the identity; e.g., the individual characteristics;â he did so using a set of test firings from .38 Special Smith & Wesson r Â evolvers. For each pair of bullets, Biasotti (1959:37â44) conducted a com- plete inventory of all striations; from this inventory, he noted that same-gun bullets yielded a greater number of corresponding marks than different-gun bullets, but he cautioned that a simple percentage of matching lines is an inappropriate measure of similarity: The average percent match for bullets fired from the same gun ranged from 36 to 38% for lead bullets and from 21 to 24% for metal-cased b Â ullets. For bullets fired from different guns . . . 15 to 20% matching lines per land or groove mark was frequently found. Relatively speaking, this data indicates that even under such ideal conditions [as the experimental test firings] the average percent match for bullets from the same gun is low and the percent match for bullets from different guns is high, which
66 BALLISTIC IMAGING should illustrate the limited value of percent matching lines without regard to consecutiveness. As frequently happens in actual practice, when there is a preponderance of non-matching lines and only a few land and groove marks available for comparison, the total number of matching lines is often no higher or even less than the number which could occur. [These results, along with those of Burd and Kirk (1942) on toolmarks generally] should dispel the erroneous conception of the âperfect matchâ which is actually only a theoretical possibility and a practical impossibility. What Biasotti (1959:44) found compelling, though, was evidence of runs or series of consecutive matching striations: It should be obvious that consecutiveness; viz., the compounding of a n Â umber of individual characteristics, is the very basis of all identities. When individual characteristics are grouped or related by the criteria of consecutiveness, which is a simplified means of expressing a correspon- dence of contour, the chance occurrence of even a very small number of consecutive matching lines (e.g., more than 3 or 4) is for all practical pur- poses impossible except as the result of a common agent, e.g., same gun. Based on subsequent research, Biasotti and Murdock (2002:224â225) for- malized a set of âconservative quantitative criteria for identification:â (1) In three-dimensional toolmarks when at least two different groups of at least three consecutive matching striae appear in the same relative posi- tion, or one group of six consecutive matching striae are in agreement in an evidence toolmark compared to a test toolmark. (2) In two-dimensional toolmarks when at least two groups of at least five consecutive matching striae appear in the same relative position, or one group of eight consecutive matching striae are in agreement in an evidence toolmark compared to a test toolmark. For these criteria to apply, however, the possibility of subclass character- istics must be ruled out. These criteria differentiate between three-dimensional marks, which Biasotti and Murdock (2002:208) characterize as contour or impression, and two-dimensional marks, described as surface or imprint. That is, two- dimensional marks are âstriae lacking depth and therefore appearing two- dimensionalâ (Biasotti and Murdock, 2002:224), giving rise to the âline â he T Biasotti and Murdock criteria were first published in 1997; no changes were made in 2002, though it was noted that in the intervening years âno known non-matching (two- or three-dimensional) toolmarks were found in [any follow-up] studies which exhibited agree- mentâ of the conservative criteria (Biasotti and Murdock, 2002:225).
FIREARMS IDENTIFICATION 67 countingâ appellation that has been applied to CMS methods. Recently, as surface metrology techniques have been applied to studying bulletsâ particularly the development of a three-dimensional-analysis system for bullets by the manufacturer of the Integrated Ballistics Identification System (IBIS) currently in useâthis distinction has come under some question (see, e.g., Thompson, 2006). Striated toolmarks necessarily have depth, how- ever slight; the availability of detailed measures of surface contours invites the question of significance levels in determining whether corresponding striations match. (We revisit the two-dimensional and three-dimensional distinction in Chapter 7.) 3âB.4â Legal Context of Firearms Examination In order to testify to their findings at trial, firearms experts are sub- jected to qualifying questions in the voir dire process. If they are favorably ruled on by the trial court judge, the expert must testify to matches (or nonmatches) of ballistics evidence based on what is ultimately a subjec- tive assessment. Molnar (1970:39) described the pressures that come with that task: [Serious criminal] cases very often never get off the ground until the fire- arms examiner has made a finding, which incidentally has to be correct, at which time the police file charges and the wheels of justice begin to grind. There is no second or reanalysis to be made, no excuses, no bad or spoiled reagents. The examinerâs area of conclusions is more often either black or white, hardly ever the grey area enjoyed by other criminalists. Others may come along to say that he was wrong, or that they canât arrive at the same conclusion, but the firearms examiner has to be RIGHT and has to say so FIRST. Consequently, firearms examiners may often express their findings in bold absolutesâmatches made to the same gun, to the exclusion of all other firearms in the worldâyet they tend to be conservative in reaching their o Â pinions. If a firearms examiner is impeached through the voir dire process, his or her ability to testify in other cases can be severely affected; being asso- ciated with an error or misidentification can tarnish reputations. ÂThornton and Peterson (2002:21) argue that this beliefâwhich they note âis not entirely without justificationââmakes forensic science, in general, resistant to proficiency testing of examiners; âthe potential exists that in court, counsel for the opposing side will in a self-serving fashion misÂconstrue, pervert and abuse a missed proficiency test.â The AFTE range of conclusions (Box 3-1) envisions four possible outcomes when an examiner is asked to compare pieces of evidence. Regardless of which of these options the examiner deems
68 BALLISTIC IMAGING fit after careful consideration, it is in keeping with the nature and weight of their testimonyâand the adversarial nature of courtroom questioningâthat their findings are expressed as unequivocal and unyielding. An examinerâs conviction in the findings about the interrelationship of evidence, and the basic admissibility of that evidence in court, depends critically on the careful maintenance of the âchain of evidence.â This begins at the crime scene itself, where the site must be preserved until an evidence technician can collect it in a safe and timely manner, maintaining its integrity. Collected evidence must not be allowed to be contaminated, lest its credibility be undermined; physical custody must be maintained and monitored throughout the laboratory examination, and processing steps should not be destructive or injurious to the physical evidence. Any break or delay in the sequence of events, or any miscommunication, may lead investigations to stall, crimes to remain unsolved, and prosecutions to lose key support. Like other branches of forensic science, firearms and toolmark iden- tification has had to grapple with the question of how well the field fits emerging standards for scientific evidence in legal proceedings. In 1923, Frye v. United States (293 F. 1013, DC Cir) observed that: Just when a scientific principle or discovery crosses the line between the experimental and demonstrable stages is difficult to define. Somewhere in this twilight zone the evidential force of the principle must be recog- nized, and while courts will go a long way in admitting expert testimony deduced from a well-recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs. The ruling established a âgeneral acceptance in the fieldâ standard that became the basis for subsequent decisions. In 1993, the U.S. Supreme Courtâs ruling in Daubert v. Merrell Dow Pharmaceuticals (509 U.S. 579) concluded that the legislatively enacted Federal Rules of Evidence superseded the Frye âgeneral acceptanceâ stan- dard. Justice Harry Blackmunâs majority opinion tasked judges with a gatekeeper role, âassess[ing] whether the reasoning or methodology under- lying the testimony is scientifically valid [and] whether that reasoning or methodology properly can be applied to the facts in issue.â More concisely, the task is the assessment of reliability and relevance. Though the opinion expressly noted that âwe do not presume to set out a definitive checklist or test,â it also identified five criteria for reliability that have since become known as the Daubert standard: (1) âwhether the theory or technique has been subjected to peer review and publication,â (2) âwhether it can be (and has been) testedâ or falsified, (3) the techniques âknown or potential rate
FIREARMS IDENTIFICATION 69 of error,â (4) âthe existence and maintenance of standards controlling the techniqueâs operation,â and (5) the Frye criterion of âgeneral acceptanceâ by the scientific community. Due to its grounding in the Federal Rules of Evidence, the Daubert standard is not binding on individual states, about half of which continue to use the Frye test. Branches of forensic science like toolmark evaluation are increasingly concerned with how their fields fit either standard, cognizant that the p Â recedent of a single ruling of inadmissibility could jeopardize future pro- ceedings. That question has grown ever greater with the Florida Supreme Courtâs December 2001 ruling in Ramirez v. State of Florida (No. SC92975). In that ruling, the court reversed the 1983 murder conviction (and death sentence) of Joseph Ramirez by excluding testimony on the toolmarks left by the knife on human cartilage. The ruling summarized the critical issue under review: Ramirez asserts that the trial court erred in allowing the Stateâs experts to testify that the knife found in Ramirezâs car was the murder weapon to the exclusion of every other knife in the world. He contends that [the toolmark examinerâs] identification method is novel and untested and the State has failed to present sufficient proof of its reliability. Moran and Murdock (2002:215) note that the court âreviewed testi- mony of five AFTE members who provided traditional justification for the identification of striated toolmarks throughout these proceedings based only on qualitative criteria established through âtraining and experience.â The court found that these explanations did not satisfy Floridaâs rigorous [Frye] standards for reliability.â The courtâs ruling concluded that âthe record does not show that [the examinerâs] methodologyâand particularly his claim of infallibilityâhas ever been formally tested or otherwise veri- fied, [nor has it] ever been subjected to meaningful peer review or publica- tion.â They concluded further that that the examinerâs claim of a match lacked documentation or substantiation and that âthe error rate for [the examinerâs] method has [never] been quantified.â For reviews in the firearms examiner literature on the applicability of Daubert criteria in the field, see Grzybowski and Murdock (1998) and Rosenberry (2003), among others. More recently, Schwartz (2005) extends what was originally an amicus curiae brief into a fuller argument as to why firearms and toolmark evidence should be ruled inadmissible in legal proceedings, to which Nichols (2005) offers a response. â lorida is one of the states in which the courts have elected to continue applying the Frye F âgeneral acceptanceâ criterion rather than the Daubert standard. However, as the quotations from the ruling suggest, the Ramirez court considered elements of the Daubert criteria.
70 BALLISTIC IMAGING 3âCâUniqueness, Reproducibility, and Permanence of Markings in Traditional Firearms Identification In recent years, several review articles have summarized the findings of individual studies on the basic principles of firearms and toolmarksâthe uniqueness, reproducibility, and permanence of individual characteristics, as seen by trained examiners using comparison microscopy. Most of these studies are limited in scale and have been conducted by firearms examiners (and examiners in training) in state and local law enforcement laboratories as adjuncts to their regular casework. The review articles attempt to piece together major themes from decades of such studies, most having been published in the AFTE Journal but also in other forensic science publica- tions. Nichols (1997, 2004) contributes a two-part narrative with the goal of characterizing the state of the field. Bonfanti and De Kinder (1999a, 1999b) review a broad array of experimental studiesâon the influence of manufacturing techniques (e.g., consecutive tooling) and the endurance of marks over repeated firings, respectivelyâdistilling the studies as entries in extensive summary tables. We draw from these review papers in this section and excerpt additional detail from individual studies, as appropriate. 3âC.1âUniqueness of Markings A fundamental assumption in firearms identification is that individual firearms vary microscopically in ways that leave unique markings on bullet and cartridge case evidence. Accordingly, the âgold standardâ for demon- strating the uniqueness of toolmarks in ballistics evidence would be sets of firearms that are consecutively manufacturedâthat is, more than one gun where every constituent part is subjected to identical tooling and machin- ing operations (e.g., minimizing the wear on cutting tools between differ- ent pieces). This is difficult to achieve in practice given the assembly-line nature of firearms manufacturing, where individual parts may be made in advance (and not necessarily at the same facility) and are drawn from bins prior to assembly. Due to the time and manufacturer cooperation needed to ensure consecutive manufacture, those studies that have been doneâas summarized by Bonfanti and De Kinder (1999a)âdeal with small numbers, typically less than 15. It is also typically the case that only one part (or â ne entry in the tables in Bonfanti and De Kinder (1999a) stands out: amidst studies O with small numbers of firearms with some level of consecutively manufactured parts, GrooÃ (1995) is reported as having examined 3,704 Walther P5 pistols. The entry is misleading in its placement in the tablesâGrooÃ makes no claim of consecutive manufacturing or serial numberingâbut the study is still interesting as a case study of a wide-scale search of evidence using conventional microscopy rather than being assisted by imaging methodology; see foot- note 17 in this chapter.
FIREARMS IDENTIFICATION 71 very few) of the guns in these studies are consecutively manufacturedâe.g., consecutively reamed barrels or machined breech faces. Several of the studies documented by Bonfanti and De Kinder (1999a) deal with firearms that have sequential serial numbers. That is, the weapons effectively came off of the assembly line consecutively. Lutz (1970:24) reiter- ated that âmere serial number sequence has no significance [in assessing the similarity of firearms], because firearm manufacturers usually have assem- bly line procedures that join the various weapons parts, without regard to actual manufacturing sequence.â Still, depending on the manufacturer and where in the process serial numbering occurs, guns that have similar serial numbers may have at least some components that were manufactured in close temporal proximity; hence, it remains popular as a weak proxy for consecutive manufacture. Bonfanti and De Kinder (1999b:Table 1) profile 27 separate studies of bullets from firearms with some indication of consecutive manufacture (or close serial numbering); these studies spanned a variety of calibers and barrel rifling techniques.10 From their review, they conclude that âfor all types of rifling no problem occurs concerning the identification of the indi- vidual firearm if certain criteria are followed.â Some firearms cannot be identified correctly solely by examination of the bullets (e.g., ÂChurchman, 1981; Lomoro, 1974; Matty, 1985), but Bonfanti and De Kinder (1999b:5) explain some of these results through their suggested criteria: âcorrespon- dence between fine striation lines in (the central part) of the land impressions must be sought,â as striations on the edges of the land engraved areas or in the groove engraved areas âmay display subclass characteristicsâ that could be confused with individual features. For instance, Lomoroâs (1974:18) test firings from different but close serial-numbered F.I.E. Titanic revolvers were very similar in groove markings but more readily distinguishable by markings in the land areas. Among more recent efforts, Brundageâs (1998) set of 10 consecutively rifled Ruger barrels is prominent because it was conducted as a blind studyâthat is, a test set of firings from the barrels, without indication of the circumstances of the underlying barrel manu- facture, was given to various firearms examiners for comparison. More recently, a set of bullets fired through consecutively manufactured Hi-Point â his concept arises in discussing experimental results in Chapter 8. In addition to being T a weak proxy for consecutive manufacture, sequential serial numbers may also suggest large batch purchases of firearms, such as the deployment of new duty firearms among police o Â fficers. In our analyses of the New York CoBIS reference ballistic image database, we encoun- ter runs of consecutively serial-numbered firearms with similar IBIS comparison scores. 10â his count excludes the GrooÃ (1995) study (see footnote 8 in this chapter) and the T Biasotti (1959) study profiled in Section 3âB.3, neither of which made explicit claims of con- secutiveness. They are included in the Bonfanti and De Kinder (1999b:Table 1) table but have no entry in the âParticularityâ column.
72 BALLISTIC IMAGING barrels (described in Beauchamp and Roberge, 2005), has become a similar proficiency test of sorts. For markings on cartridge cases, Bonfanti and De Kinder (1999b: Table 3) summarize 13 studies with some indication of consecutive man- ufacture.11 The conclusion that they derive from these studies is more nuanced than for bullets: âDepending on the firearm that was used, dif- ferent results were used [and] in a number of cases a correct identification was difficult to perform.â Among these problematic cases were the studies of Matty and Johnson (1984), Uchiyama (1986), and Lardizabal (1995), which we describe elsewhere in this chapter and in Chapter 2. Bonfanti and De Kinder found it hard to classify these problematic cases by manufactur- ing technique, but offered as âa probable solution to this problemâ a com- mon theme that recurred in several of the studies. Specifically, individual examiners noted remarkable similarities on some of the marks but found that they could make identifications using the full range of markings on the cartridge cases, not just the firing pin impression or breech face mark. Hence, Bonfanti and De Kinder (1999b:5) suggested making use of all applicable marks, including ejector and extractor marks, since âit is less likely that all these parts are manufactured consecutively and that they all bear subclass characteristics.â 3âC.2â Reproducibility and Permanence of Markings To be useful for identification, the characteristic marks left by firearms must not only be unique but reproducibleâthat is, the unique character- istics must be capable of being deposited over the multiple firings so that they can be found on recovered evidence and successfully compared with those on other items. This requirement is not the same as saying that every individual mark must be registered with equal clarity on every firing; as described in Chapter 2, the firing process depends on combustion processes and gas pressures that are inherently variable, and so will influence the exact conditions under which marks are imparted from shot to shot. But it is crucial to the theory of firearms identification that the unique marks of a firearm have a certain endurance (if not permanence) and do not change from shot to shot or change as the gun is subjected to increasing levels of wear. Bonfanti and De Kinder (1999a) summarize 10 studies from the fire- arms identification literature that addressed the effect of wear or repeated use of a firearm on the markings it left on evidence; most of the studies con- 11Again, this excludes GrooÃ (1995), which is listed in the Bonfanti and De Kinder table, as well as a few other studies in which the firearms parts in question are described as being randomly selected from production runs.
FIREARMS IDENTIFICATION 73 centrated on the effect on the striations left on bullets, while four included consideration of the markings left on cartridge cases. The numbers of shots fired in these studies range from 20 to 5,000. From the 10 studies, Bonfanti and De Kinder (1999a:319, 321) con- clude that the major cartridge case markings are relatively less vulnerable to change: âno substantial change in characteristics left by the breech face of the weapon can be discernedâ over repeated firings; firing pin impressions and extractor marks are subject to âslight variations,â while âin one study the ejector marks were seen to vary more strongly.â Bullets, by comparison, showed more dramatic effects due to wear; this is not greatly surprising given that a firearmâs barrel is subject to the most fouling (deposition of fir- ing residue) and the most metal-against-metal scraping (as the bullet Âtravels out of the barrel) of the firearmâs internal surfaces. âChanges consist of disappearing fine and coarse striation lines,â with the fine striations being more variable over time than the coarser. The composition and design of the bullet makes a great difference; simple lead bullets may be unmatchable to a first shot after 50 firings while the identifying stria left on jacketed bullets have been observed to endure for 500 or 5,000 shots. Most of these studies either compare the first to the last firings in sequence or focus on a sample of the firings: for instance, the Ogihara et al. (1989) study retained 69 bullet and cartridge case sets from the total of 5,000 firings, and their major conclusions concern the comparison between firings 1 and 5,000.12 Likewise, Hamby (1974) retained bullets from firings 1, 101, 201, 301, 401, and 501 from a M16A1 rifle; these were compared with each other in sequence (e.g., 1 to 101 and 101 to 201), as well as comparing shot 1 to shot 501.13 More recently, Vinci et al. (2005) examined a set of exhibits consisting of every 100th round in a sequence of 2,500 firings of 230 grain FMJ Giulio Fiocchi Lecco ammunition through a .45 caliber HP (ADLER customized) semiautomatic Springfield Armory pistol. Batches of 100 firings were per- formed at separate times; âthe pistol was disassembled, cleaned and oiled after each 100 round firing session in respect of findings previously reported that accumulated residue on the weapon can affect the [breech face] marks on cartridgesâ (Vinci et al., 2005:369, citing findings from Molnar, 1977; see Section 3ÂâD.1). Vinci et al. (2005:371) concluded that âthere was a slight observable modification in the quality of the marksâ over the long firing, but that âthe gun could still be identifiedâ even in the late-stage 12â gihara O et al. (1989) retained every 10th shot from firings 1â100, every 50th shot from firings 150â1,000, and every 100th shot from firings 1,100â5,000. 13â amby (1974) chose the particular rifle because it was known to generate high pressures H during firing, âwhich should hasten the barrel wearing process.â The specific gun had already been fired âapproximately 40,000 times.â The barrel was not cleaned at any point during the test firings.
74 BALLISTIC IMAGING exhibits. However, the breech face marks were ânot useful for matching any of the 2500 cartridges to the weaponâ because the presence and clar- ity of these marks were inconsistent. Firing pin impressions proved more useful although, âafter round 70, the nose of the firing pin was beginning to lose its imperfections resulting in a small flattened circular area at the bottom of the marks. Although firing pin drag marks were not consistently produced throughout the 2500 round firing sequence, the last 200 rounds did contain sufficient stria to match the cartridges to the weapon.â Mean- while, the value of ejector marks to making identifications âwas enhancedâ over repeated firing; the size and depth of the ejector mark increased âafter firing 600 rounds.â In comparison with these longevity studies, Uchiyama et al. (1988) completed a rarer study of actual shot-to-shot variability for a string of 100 firings. Specifically, they collected bullets and cartridge casings from each of the 100 test firings, divided between four different combinations of gun brand and caliber. Each markâland areas on the bullets and breech face and firing pin marks on the cartridgesâwas examined separately by examiners to assess the quantity of unique, individualizing lines or features. Each mark was then assigned an identifiability score of 1, 2, or 3; 1 indi- cated few or no identifiable features and 3 indicated sufficient features to support an identification based on that mark alone. Each bullet and casing was then assigned a score corresponding to the maximum identifiability score of its constituent marks. The analysis stopped short of true shot-to- shot comparison of features, although this was done for some sequences of well-marked (identifiability score 3) bullets. For centerfire cartridges, they observed an approximately 10â50â40 per- cent division across identifiability grades 1, 2, and 3, respectively. Breech face marks generally showed higher identifiability scores than firing pin marks, which Uchiyama et al. (1988:378) attribute to the greater surface area of the breech face marks; however, for firings from a .38 Special Smith & Wesson (for which âthe surface of the breech face is rather smooth and the firing pin is large and has irregular markingsâ), firing pin marks outperformed breech face. Identifiability scores dropped markedly for rimfire cartridges, with only about 5 percent having score 3 and 35 percent score 1; none of the breech face markings for rimfire casings was judged to have identifiability level 3. For bullets, identifiability level 3 ranged from 20 to 60 percent across the different gun/caliber combinations, and Uchiyama et al. (1988) judged that none of the test-fired bullets fell into identifiability level 1. Blackwell and Framan (1980:16) cite discussions with an examiner at the Los Angeles Police Department in suggesting a âreproducibility spec- trum,â a continuum of manufacturing standards and firearms user practices that can affect the reproducibility of individual marks. At one extreme are police officers, for whom a firearm is such a vital part of their equipment
FIREARMS IDENTIFICATION 75 that they â[develop] pride and interest in maintaining it in superior working condition.â However, this âconstant attention to cleaning and polishingâ serves to âcompletely obliterate many, if not all, of the original identifying imperfections in the bore.â âMany officers mount their pistols in a drill press and actually wire-brush the bore to the point that individual features originally in the bore are removed, and new ones created.â Military small arms represent the other end of the spectrum: These firearms, because of the nature of mass production, frequently retain their identifying characteristics for the life of the firearm. During manufacture, the bores are not carefully polished or lead lapped and the small blemishes that cause striations are retained virtually unchanged. Subsequent perfunctory or even diligent cleaning frequently does not oblit- erate them. âThe firearms that most frequently find their way into the firearms identi- fication laboratoryâ fall in between these two extremes. From the available studies of the reproducibility and endurance of firearms toolmarks, it is difficult to conclude that any of the markings are inherently more reliable than others. De Kinder (2002a:200) argued that âthe breech face of the firearm seems to provide the most stable trace on the components of the fired roundâ and hence suggested that it might be the primary mark collected in a large-scale reference ballistic image data- base (RBID). However, he also observed that âimportant similarities were seen between marks left by the breech faces of subsequently manufactured firearmsââthat is, the breech face may be prone to subclass carry-over effectsâand so an RBID would likely have to include other marks like the firing pin. Likewise, Tulleners (2001:3-2) wrote that, âfor automated imag- ing, the only areas used are the firing pin impressions, breech face marks, and ejector marksâ because âthese are the marks that are typically repeat- able.â However, âin most cases the firing pin may not leave sufficient detail for analysis and most examiners rely on the breech face marksâ to make identifications (Tulleners, 2001:3-2). 3âDâ Challenging Situations in Firearms Identification Over the course of years of analysis, forensic firearms examin- ers encounter numerous situations that complicate identification. These may be deliberate measures taken by the shooterâcountermeasures to identificationâbut they may also be mechanical problems in firing. Smith (1971) cataloged 24 such situations, which he dubbed âjokersâ in the field of firearms identification. He suggested that the top 10 such complications, âin the approximate order of frequency of occurrence,â are:
76 BALLISTIC IMAGING â¢ automatic pistol bullets fired from revolvers; â¢ pistol bullets fired from rifles by using adapters; â¢ pistol bullets fired from rifles after being handloaded into rifle car- tridge cases; â¢ revolver-type bullets fired from automatic pistols; â¢ replacement of barrel of an automatic pistol with another; â¢ replacement of firing pin in automatic pistol; â¢ refiling of breech face of automatic pistol or revolver; â¢ refiling firing pin of automatic pistol or revolver; â¢ replacing revolver barrel (which is more difficult than with more modular semiautomatics); and â¢ relining a pistol or rifle barrel with a new rifled liner. Other complications include âfiring a bullet of one caliber through an arm chambered for a larger caliberâ (âsuch a bullet will show sketchy and erratic rifling marks which will be of little help in establishing identifica- tionâ) and âfiring a pistol or revolver cartridge through a smooth bored barrelâ (âthe bullet will obviously show no rifling marksâ). In this section, we briefly review what has been discussed in the fire- arms identification literature about some of these challenging situations. It is not an exhaustive list but covers particular topics that are more germane to RBIDs containing images from new firearms. 3âD.1â Condition of Evidence: Damage, Corrosion, and Cleanliness In forensic laboratories, firearms can be discharged into water tanks (or other nondestructive trap mechanisms) so that bullets may be recov- ered with no damage other than those left by the firing process; similarly, cartridge casings may be quickly and safely retrieved following controlled test firings. A basic, fundamental challenge of firearms identification is that crime scenes are not necessarily such controlled settings. The task of pattern matching between pieces of bullet or cartridge case evidenceâconsidering which microscopically fine markings may be unique to the source firearm, filtering out other marks, and evaluating various possible alignments of the exhibits (including, for bullets, all possible rotations of the exhibit pairs)âis already a difficult one. But it can be made more difficult by the nonpristine nature of crime scene evidence. Bullets can strike wood, asphalt, human tissue and bone, or other substances and, consequently, can be seriously warped, deformed, or fragmented; they can be lodged such that even their recovery for analysis can cause damage. Likewise, cartridge casings expelled onto the ground may be crushed underfoot or exposed to the elements. The possible differences between pristine exhibits and crime-scene samples are a continuing challenge for conventional firearms identification and ballistic
FIREARMS IDENTIFICATION 77 imaging techniques, particularly in the context of an RBID for which the basic point is the comparison of crime scene evidence with a pristine sample from a gun in brand-new condition. Because the basic theory underlying firearms identification is that fine microscopic imperfections on the surface of internal parts of a firearm impart those marks on bullets and cartridge cases fired in them, it also follows that abrasion and erosion of the firearmâs internal parts can change the unique marks left on ballistics evidence. Gun users vary in the degree of care and maintenance they give to their fire- arms, from meticulous cleaning to neglect. Hence, guns generallyâand the subset of guns used in crimeâare subject to different levels of residue and dirt build-up and to different levels of corrosion. Corrosion âis the rusting or the eating away of the metal by some chemical action. This condition is usually due to firing ammunition loaded with corrosive Âprimers and to improper care of a gun between the times it is usedâ (American Institute of Applied Science, 1982:81). Fouling and barrel cleanliness are prominent concerns in the analysis of bullet striations, given the tendency for residue and metal scrapings to build up in the barrel. It might be expected to be a relatively minor concern for the markings on cartridge cases, but Molnar (1977:21) advised examiners that this is not necessarily the case. âAn examination of the breech face is in orderâ in cases where âyou are having trouble with a firearm that is not reproducing breech face marks on the primer or cartridge cases on your tests,â he wrote. âOn many occasions the fouling of previous shots have built up to such an extent that the accumulated crud obliterates the breech face mark configurations to such an extent that their impressions on the primers are affected and sometimes precluded. On small caliber guns with low chamber pressures, even a few unburned powder granules adhering to the breech face can cause amazing differences in registrations, even altering some characteristics.â Tulleners (2001:3-2) makes a similar observation, noting that âdirt or lead build up on the breech face can reduce the detail of breech face impressions.â Hess and Moran (2006:112) observed that, âperiodically, firearms examiners and [IBIS] technicians receive requests to examine firearms that have been oxidized (rusted) and/or corroded due to a variety of factors.â This corrosion can be so pronounced as to make it difficult to operate and test fire the weapon. Moreover, âany test firing conducted while the firearm is in this condition risks permanent alteration of the weaponâs signature on these working surfaces for purposes of IBIS entry and future comparison,â and test-fired evidence from a corroded weapon may not match evidence already on file in databases. They conclude that, âgiven the backlog that most agencies are facing in this time of budget restraints, increasing caseloads, and understaffing in firearms units across the country, the probability that firearms received in corroded condition will not be test
78 BALLISTIC IMAGING fired at all is likely,â missing possible hits. Corrosion is also problematic because some means of dealing with itâincluding scrubbing with metal or other brushesâmay also damage the weapon for the purposes of generat- ing matchable marks. Corrosion is a concern not only for the internal parts of firearms, but also for recovered ballistics evidence. Though it is certainly ideal to process and collect evidence from crime scenes rapidly, such is not always possible. Bullet and cartridge case evidence may be exposed to the elements for days, weeks, or months until they are found and recovered, and bullet evidence may be irretrievable from shooting victims because rapid extraction could be harmful to their health. See Larrison (2006) for a study of the rate of degradation of bullets and cartridgesâmonitored every 6 months over 2 yearsâin four different and demanding environmental conditions: soil, water, open air, and an animal carcass. 3âD.2â Countermeasures Smithâs (1971) listing of âjokers,â which introduced this section, includes some deliberate countermeasures that might be taken by criminalsâperhaps after firing a lethal shotâto try to mislead investigators. Aside from Smithâs rough ordering of situations by frequency and the rough impressions formed by examiners over their years of experience, there are no firm and system- atic data on the frequency with which criminals deliberately alter firearms parts (or attempt to obliterate serial numbers) in order to avoid detection. Some countermeasures, like crude filing of the barrel, are relatively easy to perform (if not always effective).14 As Smith (1971) articulates in fleshing out his list of problematic situations, some countermeasures are particularly rare because they are inherently more difficult to perform. The barrel of a revolver, for instance, is a more integrated part of the firearm assembly than the more modular barrel of a semiautomatic, so swapping out a revolver barrel requires special tools and considerable knowledge. With expert knowledge, the range of countermeasures that might be taken is immense. For instance, Schecter et al. (1996:97) concluded that it was possible to replace the entire breech block of a SIG Sauer P226 9mm Luger pistol, so that âonly the ejector will remain to give possible indi- vidual marks on the cartridge case base area from the âoriginalâ weapon.â However, the registration of âgood ejector and chamber marks on weapons 14â f course, it is possible for quick measures to be very effective at changing toolmarks. At O the committeeâs December 2004 meeting, firearms examiner Lucien Haag shared an evocative presentation entitled ââNewâ Bores and Breechfaces in 60 Seconds,â which suggests two quick ways in which a knowledgeable user could rapidly alter the striations left by the barrel or the breech face markings left on cartridge casings.
FIREARMS IDENTIFICATION 79 of this quality can be poor to non-existent,â and this technique would not be immediately obvious on inspection of the weapon. But the issue is how often people who use guns in crime would go to such lengths, akin to the proverbial question of why more criminals do not wear gloves while com- mitting crimes (given the ease of leaving fingerprints). Smith (1971:18) argued that replacing pistol barrels âmay happen not infrequently;â he personally reported having seen two such cases in criminal cases.15 He, however, ânever personally encountered [a case of replacing a firing pin in an automatic pistol], and it is obvious that such replacement of other parts, (extractor and ejector), refiling of breech face exists, still the possibility of the replacement of this part alone must be kept in mindâ (Smith, 1971:19). Refiling the breech face is problematic, but âmuch refil- ing would leave the breech surface bright & fresh in appearanceâ; for full concealment, âit would be much simpler to discard the arm entirely and replace it with another, rather than go to the effortâ to make it appear that an arm with a refiled breech face had not been altered (Smith, 1971:19). It should be noted that while some countermeasures may successfully alter the âsignatureâ markings left on ballistics evidence, they also serve to create new sets of markingsâand, in some instances, prominent signs of the alterationâthat can be used to match to evidence from later cases. Konior (2006) describes a case in which three cartridge casings and a pistol were recovered in investigating a homicide. The evidence casings did not appear to match test firings from the firearm; the latter all showed much greater levels of flowback around the firing pin impression. Subsequent analysis determined that an attempt had been made to alter the firearm by drilling the entire length of the pistolâs barrel; however, the person attempting the modification apparently inserted the drill bit into the firing pin aperture, widening the hole but also damaging the tip of the firing pin. The flowback and a new distinctive mark in the firing pin impression could be attributed to this attempted modification. 3âD.3â âSettle-Inâ Effect From the standpoint of establishing an RBID, a phenomenon of extreme interest is what might be called a âsettle-inâ or âbreaking-inâ effect: the notion that it takes several firings for a firearmâs unique, characteristic markings to stabilize. When the settle-in effect has been documented, it 15â n this context, Smith (1971:18) notes that the interchangeability of barrels was made vivid I âin the famous Sacco-Vanzetti case.â Specifically, âthe barrel of the fatal arm was, following a demonstration before the court by an expert for the defense, found present in one of the two other arms of the same type which had been introduced as exhibits, all three having been disassembled and reassembled in the course of the demonstration.â
80 BALLISTIC IMAGING has been almost exclusively in the context of the striations left on bullets and not on markings left on cartridge cases. Thisâin addition to the time- intensive process of firing into a water tank or other nondestructive trap and retrieving individual bulletsâis a major reason that the restriction of RBIDs to cartridge case entries is sensible. Murdock (1981:90) analyzed 10 test-fired bullets from each of three new and consecutively rifled barrels. He found that, âin general, the com- parison between the first, second, and third firing from any one barrel failed to result in an identification. Some good agreement was present, however. The third, fourth, and fifth test firings from any one barrel could, however, generally be identified as having been fired through the same Âbarrel.â From this, âit became obvious that each barrel needed to have a few Â bullets fired through it before it began marking in a reproducible, identifiable m Â anner.â Similar work by Hall (1983:43) using a set of consecutively reamed Âpolygonal barrels noted ârapid change during the first few shots,â so that firings 1 and 2 from the same barrel looked much different com- pared to each other than did firings 19 and 20. Hall found a âlack of iden- tifications where bullets from any of the first five shots were compared to any others.â Matty (1985:65) noted similar behavior but was not as precise in suggesting the number of firings after which individual characteristics were discernible; instead, he observed that âit was not possible to make a conclusive match between test bullets #1 and #2 [from the same barrel, but] bullets #9 and #10 . . . were very similar in appearance.â From these and other works, Bonfanti and De Kinder (1999a:5) con- cluded that âabout five to nine shotsâ are needed âso that [barrels] transfer a signature to a bullet.â They note that the studies of consecutively manu- factured barrels that they summarize in their review meet this standard. However, at least one of those studiesâwork by Lutz (1970:25) using two new and consecutively manufactured .38 Special Smith & Wesson barrelsâ began with the barrels in a completely unfired state and downplays any settle-in effect. Indeed, Lutz described the completely unfired nature of the barrels as the key advantage of the study, as it âoffer[s] the ultimate as far as similarities between two successive barrels. It is certain that the similar markings visible now would become less prominent after being subjected to normal firing, cleaning, and wear.â Even though all the test firings Lutz examined were among the first 12 uses of the barrel, âsufficient matching individual striae were noted on the bullets to enable the examiners to eas- ily identify the barrel of origin for each of the bullets. Similarities in class characteristics were noted; however, microscopic comparison of the bullets revealed that each barrel had caused different markings to such an extent that each land and groove impression on each of the bullets had a great number of individual identifying striae.â Though a prominent settle-in effect for the breech face or firing pinâ
FIREARMS IDENTIFICATION 81 the prominent markings on cartridge casesâhas not been documented, there may be structural or design features that may cause a similar effect. The Thompson (1996) investigation of highly similar marks resulting from different Lorcin L9 9mm pistols (see Section 2âD.1) included some firings from guns right off the manufacturing line, with no previous proof firing. It was noted that the âbreech face impression . . . can change considerably shot-to-shot [in early firings] due to the paint wearing/chipping off.â 3âEâ Commentary As detailed in Chapter 1, it is not the function of this committee to assess the general validity of firearms identification and toolmark exami- nation nor their admissibility in court proceedings. The discussion in this chapter on the nature of toolmark evidence and the context in which it is applied, as well as an overview of existing research among firearms exam- iners on the uniqueness and reproducibility of toolmarks, is presented to frame the discussion in the rest of this report. For instance, understanding situations that may pose particular challenges for associating two images of evidence requires some knowledge of situations that are generally known to be complex in the field; likewise, recommendations for the setup and maintenance of any ballistic imaging system that would do harm to the maintenance of clear chain of custodyâso important in the legal context of toolmark evidenceâwould be ill-advised. However, as we also note in Chapter 1, we understand that some readers may try to infer a positionâa leaning, one way or the otherâbased on the preceding analysis. Accordingly, we believe it important to make the committeeâs finding clear and unambiguous: Finding: The validity of the fundamental assumptions of uniqueness and reproducibility of firearms-related toolmarks has not yet been fully demonstrated. There is one baseline level of credibility, however, that must be demon- strated lest any discussion of ballistic imaging be rendered mootânamely, that there is at least some âsignalâ that may be detected. In other words, the creation of toolmarks must not be so random and volatile that there is no reason to believe that any similar and matchable marks exist on two e Â xhibits fired from the same gun. The existing research, and the fieldâs gen- eral acceptance in legal proceedings for several decades, is more than ade- quate testimony to that baseline level. Beyond that level, we neither endorse nor oppose the fundamental assumptions. Our review in this chapter is notâand is not meant to beâa full weighing of evidence for or against
82 BALLISTIC IMAGING the assumptions, but it is ample enough to suggest that they are not fully settled, mechanically or empirically. Another point follows directly: Additional general research on the uniqueness and reproducibility of firearms-related toolmarks would have to be done if the basic premises of firearms identification are to be put on a more solid scientific footing. A designed program of experiments covering a full range of sources of variability is important to test the fundamental assumptions, as well as to better document phenomena like âsettle-inâ effects. In such a program, it could be useful to study the level of agreement of marks generated by the whole system of parts that make up a firearm, rather than treating each mark type in isolation. For example, in a large number of test firings, how comparable is the quality of breech face mark- ing with firing pin impressions, and how do those compare with the clarity of striations etched on bullets? Fully assessing the assumptions underlying firearms identification would require careful attention to statistical experi- mental design issues, as well as intensive work on the underlying physics, engineering, and metallurgy of firearms, but is essential to the long-term viability of this type of forensic evidence. A third point is important in reading this reportâstopping short of commenting on whether firearms toolmark evidence should be admissible: Conclusions drawn in firearms identification should not be made to imply the presence of a firm statistical basis when none has been demonstrated. Specifically, as described in Section 3âB.4, examiners tend to cast their assessments in bold absolutes, commonly asserting that a match can be made âto the exclusion of all other firearms in the world.â Such comments cloak an inherently subjective assessment of a match with an extreme prob- ability statement that has no firm grounding and unrealistically implies an error rate of zero. Thornton and Peterson (2002:24â25) note the basic flaw in this reasoning: Since the basis of all forensic identification is probability theory, examiners can never really assert a conclusion of an âidentification to the exclusion of all others in the world,â but at best can only assert a very small (objec- tive or subjective) probability of a coincidental match. . . . It is ironic that those areas of forensic science that have real underlying data offer more modest statements of individualization, while those limited to subjective or impressionistic data make the strongest statements, sometimes of absolute certainty. As described in Box 3-4, recent court decisions in which admissibility of firearms toolmark evidence was in question have generally accepted that the field has validity but have refused to accept âexclusion of all other fire- armsâ arguments. The committee agrees with the basic point: statements
FIREARMS IDENTIFICATION 83 BOX 3-4 Recent Court Decisions: âTo the Exclusion of All Other Gunsâ As part of a larger trial on racketeering, assault, and gun charges, Judge Nancy Gertner of the U.S. District Court for Massachusetts rejected a motion to exclude ballistics evidence but strictly limited the scope of the testimony (United States v. Green, 405 F.Supp. 2d 104; 2005 U.S. Dist. LEXIS 34273). Fourteen .380 caliber shell casings were recovered from two sites in September 2000, six of them at the site of a shooting; about a year later, a loaded .38 caliber pistol was found in the front yard of a residence. As part of the trial, prosecutors wanted to introduce testimony from a Boston Police Department sergeant that all of the casings came from the same gun, namely, the recovered pistol. At a preliminary hearing, the sergeant indicated that he could make this determination âto the exclusion of every other firearm in the world.â Gertnerâs opinion noted that the âexclusion of every other firearm in the worldâ claim was âneedless to say, extraordinary, particularly given [the sergeantâs] data and methodsâ: the examiner âtook no notes, recorded no measurements, made no photographs, and drew no diagrams.â After reviewing toolmark issues in some detail, the court concluded: [The examiner in question] is a seasoned observer of firearms and tool- marks; he may be able to identify marks that a lay observer would not. But while I will allow [him] to testify as to his observations, I will not allow him to conclude that the match he found by dint of the specific methodology he used permits âthe exclusion of all other gunsâ as the source of the shell casings. Separate rulings in United States v. Monteiroâalso from the U.S. District Court for the District of Massachusetts, and coming before and after the Green rulingâadopted similar stances on testimony âto the exclusion of all other fire- arms.â Defendants in Monteiro challenged the specific examiner (a Massachusetts State Police sergeant) as not being qualified in firearms identification; challenged firearms identification as unreliable under Daubertâ; and asserted thatâeven if fire- arms identification were reliableâthat the examiner did not apply the techniques properly. The defense also challenged the validity of any identification because the examiner replacedââamong other partsâââthe firing pin, recoil spring, barrel, and trigger lever (but, significantly, not the breech face)â of the gun in order to get it back into firing condition. Prior to Green, Judge Patti Saris ruled on a motion to exclude ballistics evi- dence (2005 U.S. Dist. LEXIS 39062), allowing testimony in part but giving the government âtwo weeks to ensure that its proffered firearms testimony comported with the established standards in the field.â As in Green, no notes or photographs were made on the identification: Saris ruled that âuntil the basis for the identifica- tion is described in such a way that the procedure performed by [the sergeant] is reproducible and verifiable, it is inadmissible under Rule 702.â Saris further continued
84 BALLISTIC IMAGING BOX 3-4 Continued directed that the identification be subjected to independent review and verification in order to be admissible. Judge Sarisâ subsequent ruling on the general challenge to firearms identifica- tion (407 F.Supp.2d 351, 2006) concluded that âthe underlying scientific principle behind firearm identificationâthat firearms transfer unique toolmarks to spent cartridge casesâis valid under Daubert. However, the process of deciding that a cartridge case was fired by a particular gun is based primarily on a visual inspec- tion of patterns of toolmarks, and is largely a subjective determination based on experience and expertise.â The court ruled that the government must demonstrate basic standards for the qualification of the examiner. However, like Judge Gertner, Saris precludedâin any eventâany testimony of a match to the exclusion of all other guns in the world. Saris noted that âexaminers testified to the effect that they could be 100 percent sure of a match,â a statement that could not be sustained. An examiner may âtestify to a reasonable degree of ballistic certainty,â but âan expert may not assert any degree of statistical certainty, 100 percent or otherwise, as to a match.â Most recently, in United States v. Diaz (2007 U.S. Dist LEXIS 13152), Judge William Alsup of the U.S. District Court for the Northern District of California a Â ccepted that: the theory of firearm identification . . . is reliable under Daubert. While there is some subjectivity involved, it is the subjective judgment of trained professionalsÂ with a keen practiced eye for discerning the extent of match- ing patterns. . . . The record, however, does not support the conclusion that identifications can be made to the exclusion of all other firearms in the world. Thus, the examiners who testify in this case may only testify that a match has been made to a âreasonable degree of certainty in the ballistics field. In defense of firearms identification, Alsup remarked: It is important to note thatâat least according to this recordâthere has never been a single documented decision in the United States where an incorrect firearms identification was used to convict a defendant. This is not to say that examiners do not make mistakes. The record demonstrates that examiners make mistakes even on proficiency tests. But, in view of the thousands of criminal defendants who have had an incentive to challenge firearms examinersâ conclusions, it is significant that defendants cite no false- positive identification used against a criminal defendant in any American jurisdiction.
FIREARMS IDENTIFICATION 85 on toolmark matches (including legal testimony) should be supported by the work that was done in the laboratory, by the notes and documentation made by examiners, and by proficiency testing or established error rates for individual examiners in the field and in that particular laboratory, but should not overreach to make extreme probability statements. 3âFâ Role of Imaging in Firearms Identification In the next several chapters, we explore the current state of ballistic imaging technology. As context for this discussion, we note that imaging and photography have a long and somewhat controversial history in tradi- tional firearms identification. Moran (2003) summarizes some of the historical debate over the use of comparison photographs, culling relevant quotations from source Âmaterials. Some of the pioneers of the field of firearms identificationâGoddard, B Â urrard, and Hatcherâconsidered photography to be valuable, if not essen- tial, Burrard going so far as to comment that âany evidence unsupported by photographs cannot be regarded as being anything more than an expression of opinion. Photographs are, accordingly, essential; and such as are deemed necessary must be taken through the microscopeâ (Moran, 2003:175). However, Hatcher sounded a note of concern: âThere is a difference in the ability of the various experts to use the microscope and camera, so that in the hands of a very skilled operator they may show the correspondence or lack of correspondence very clearly, while in the hands of a poor or mediocre operator, they may show the same thing faintly, or may even fail to show them at allâ (Moran, 2003:176). However, with the passage of time, the practice of using photographs to document identifications fell out of favor, so much so that a 1957 revision of Hatcherâs 1935 text now stipulated that âphoto micrographs are now rarely used,â for a variety of reasons (Moran, 2003:177): â¢ Courts tended to accept examinersâ testimony on identifications without the âvisual proof,â obviating the need to prepare the photographs. â¢ Preparation of the photographs took time, time that laboratories were unwilling to commit due to increased caseloads. â¢ Static views of an evidence match were deemed unsatisfactory, relative to the full range of panning and rotation possible during direct manipulation of the evidence. â¢ âThese pictures were not understood by juries,â and âa good deal of knowledge and experience are necessary to evaluate them.â â¢ âSome men after years of working in Firearms Identification refuse to make a positive identification from pictures alone.â
86 BALLISTIC IMAGING â¢ Photographs depict striations and features that do not match as well as those that do, which could create doubt among jurors. In subsequent decades, the use of photographs as part of documenta- tion remained a matter of personal and agency tastes, with some favoring it and others opposing it: for example, Heard (1997:113) stated that âthe use of comparison photomicrographs in a court of law to illustrate stria comparisons should be discouragedâ (although he suggested that a video might be more informative). Ultimately, in 2005, the AFTE membership approved a âstandardization of comparison documentationâ stipulating that âphotography is the preferred method of documentationâ but noting that other forms of documentation (including ânarrative descriptionsâ) âmay serve to satisfy the requirements of this standard.â This standard, revised as of June 13, 2005, was promulgated in a 2006 issue of the AFTE Journal (Vol. 38, No. 1). Prior to the use of automated ballistic imaging, law enforcement agen- cies such as the Los Angeles Police Department (LAPD) relied on cruder meansâand a certain amount of luckâto make connections with evidence in their open case files. Quite literally, making those connections depended on reference to Polaroid photomicrographs, posted on a bulletin board or shared with colleagues, in order to jog memories and generate possibilities. As of 1994, the process used by the LAPD was to post Polaroid images on two walls in âa hallway that we pass through constantly. On one side are the âunknowns,â like cartridge cases collected as evidence at a homicide scene. On the other side are âknowns.â When we recovered a gun from a suspect or a crime scene, we test-fire it in the labâthat makes it a known. . . . When we get a new known, we compare it to all the unknowns. When we get a new unknown, we compare it to all the knowns and all the unknowns,â and the pictures are added to the hallway for future reference (Maruoka, 1994b:214).16 The next chapter begins to describe efforts to go beyond Polaroids in the hallway: to use computer imaging to make it possible to more readily draw connections with exhibits in other open cases.17 16â he T Maruoka article is, in fact, a reprint in the AFTE Journal of a profile written for the Polaroid Corporationâs Instant Evidence newsletter for law enforcement officials, circulated in 1993. As such, it touts the specific Polaroid equipment and film used for the standard imaging. 17â s an example of the way a large-scale search of exhibits is conducted using conventional A methods, without imaging assistance, GrooÃ (1995:29, 30) describes a series of three mur- ders in West Germany in 1984â1985. Cartridge cases from the second and third crimes were easily matched by examiners but the cases from the first crime bore only limited similarity in markings to the others. Still, the headstamp information on the casings from all three crimes, and the bullet evidence, strongly suggested that a member of the police might be the killer. So strong was this suspicion to investigators that all 7,862 Walther P5 duty pistols then in use by the police forces throughout the state of Baden-WÃ¼rttemberg were test fired and the cartridges
FIREARMS IDENTIFICATION 87 compared with the crime scene exhibits. âAs the comparison work in this specific case [was done] using conventional microscopes,â it âwas very complicated and time-consumingâ; up to 3 firearms examiners at a time worked continuously on the comparisons. Ultimately, test-fired casings from the 3,704th pistol in sequence matched the casings from the second and third murders; this led investigators to an officer in Stuttgart who was ultimately found dead in southern Italy, having also murdered his wife and sons. GrooÃ concluded that the experience was strong testament to âthe individuality of marks on fired bullets and cartridge casesâ: that the German examiners were able to observe âmarks . . . which left no doubt that they were identical to those observed on the evidence ammunition,â against a backdrop of âapproxi- mately 4000 pistols of the same manufacturer, same model, approximately the same age and same degree of wear.â Apparently, the comparisons with test-fired exhibits were halted with the positive result on the 3,704th pistol, even though the linkage to the casings from the first murder was unclear. Even when the officerâs pistol was recovered and test fired with a variety of ammunition brands, no casing could be generated that matched the evidence from the first murder. It was originally suspected that the pistol âgot a new blue finishâ (a refurbishing process that may affect the marks left by the gun) at a time between the first and second murder, which might explain the differences. However, âa more careful examination showed that the pistol had been blued in the period between the second and third murderâ (why this did not impede the ability to match the second and third crimes is left unspecified). It was also speculated that the officer might have deliberately planted a different casing at the first crime scene to mislead detectives.