Skip to main content

Currently Skimming:

5 Descriptions of Some Forensic Science Disciplines
Pages 127-182

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.


From page 127...
... As such, there is considerable discussion about the reliability and precision of results -- attributes that factor into probative value and admissibility decisions. It should be recalled, however, that forensic science also provides great value to law enforcement investigations, and even those forensic science disciplines whose scientific foundation is currently limited might have the capacity (or the potential)
From page 128...
... Many forensic science methods have been developed in response to such evidence -- combining experiencebased knowledge with whatever relevant science base exists in order to create a procedure that returns useful information. Although some of the techniques used by the forensic science disciplines -- such as DNA analysis, serology, forensic pathology, toxicology, chemical analysis, and digital and multimedia forensics -- are built on solid bases of theory and research, many other techniques have been developed heuristically.
From page 129...
... For example, blood is not always red, some red substances are not blood, and most biological evidence, such as saliva or semen, is not readily visible. Crime scene investigators locate biological evidence through tests that screen for the presence of a particular biological fluid (e.g., blood, semen, saliva)
From page 130...
... for forensic usage: Performance testing of fluorescent multiplex STR systems and analysis of authentic and simulated forensic samples. Journal of Forensic Sciences 46(3)
From page 131...
... and are searched against DNA profiles already in one of three databases: a convicted felon database, a forensic database containing DNA profiles from crime scenes, and a database of DNA from unidentified persons. Sometimes the evidence dictates testing just for Y STRs, which assesses only the Y (male)
From page 132...
... Casework reviews of mtDNA analysis suggest a wide range in the quality of testing results that include contamination, inexperience in interpreting mixtures, and differences in how a test is conducted.10 Reporting of Results FBI quality guidelines require that reports from forensic DNA analysis must contain, at a minimum, a description of the evidence examined, a listing of the loci analyzed, a description of the methodology, results and/or conclusions, and an interpretative statement (either quantitative or qualitative) concerning the inference to be drawn from the analysis.11 10  Personal communication, Terry Melton, Mitotyping Laboratory.
From page 133...
... This power likely can be improved by strengthening the methods' scientific foundations and practice, as has occurred with forensic DNA analysis. ANALYSIS OF CONTROLLED SUBSTANCES The term "illicit drugs" is widely used to describe abused substances.
From page 134...
... Their standards are being widely adopted by drug analysis laboratories in the United States and worldwide. Sample Data and Collection Controlled substances typically are seized by police officers, narcotics agents, and detectives through undercover buys, raids on drug houses and clandestine drug laboratories, and seizures on the streets.
From page 135...
... Summary Assessment The chemical foundations for the analysis of controlled substances are sound, and there exists an adequate understanding of the uncertainties and potential errors. SWGDRUG has established a fairly complete set of recommended practices.16 It also provides pointers to a number of guidelines for statistical sampling, both for illegal drugs per se (created by the European Network of Forensic Science Institutes)
From page 136...
... Friction ridge analysis shares similarities with other experience-based methods of pattern recognition, such as those for footwear and tire impressions, toolmarks, and handwriting analysis, all of which are discussed separately below. Friction ridge analysis is performed in various settings, including accredited crime laboratories and nonaccredited facilities.
From page 137...
... The IAI also offers a certification test that measures both the knowledge and skill of latent print examiners; however, not all agencies require latent print examiners to achieve and maintain certification. Method of Data Collection and Analysis The technique used to examine prints made by friction ridge skin is described by the acronym ACE-V: "Analysis, Comparison, Evaluation, and Verification."19 It has been described in forensic literature as a means of comparative analysis of evidence since 1959.20 The process begins with the analysis of the unknown friction ridge print (now often a digital image of a latent print)
From page 138...
... 2002. Friction Ridge Examination Methodology for Latent Print Examiners.
From page 139...
... , the assessment of latent prints from crime scenes is based largely on human interpretation. Note that the ACE-V method does not specify particular measurements or a standard test protocol, and examiners must make subjective assessments throughout.
From page 140...
... with an experienced latent print examiner enables a new examiner to develop a sense of the rarity of features and groups of features; the rarity of particular kinds of ridge flows; the frequency of features in different areas of the hands and feet; the degree to which differences can be accounted for by mechanical distortion of the skin; a sense of how to extract detail from background noise; and a sense of how much friction ridge detail could be common to two prints from different 24  See, e.g., E Gutiérrez, V
From page 141...
... 2002. Friction Ridge Examination Methodology for Latent Print Examiners.
From page 142...
... Claims of ‘absolute' and ‘positive' identifica tion should be replaced by more modest claims about the meaning and significance of a ‘match.'28 Summary Assessment Historically, friction ridge analysis has served as a valuable tool, both to identify the guilty and to exclude the innocent. Because of the amount of detail available in friction ridges, it seems plausible that a careful comparison of two impressions can accurately discern whether or not they had a common source.
From page 143...
... At the very least, sufficient documentation is needed to reconstruct the analysis, if necessary. By documenting the relevant information gathered during the analysis, evaluation, and comparison of latent prints and the basis for the conclusion (identification, exclusion, or inconclusive)
From page 144...
... The impression left by a given finger will differ every time, because of inevitable variations in pressure, which change the degree of contact between each part of the ridge structure and the impression medium. None of these variabilities -- of features across a population of fingers or of repeated impressions left by the same finger -- has been characterized, quantified, or compared.35 To properly underpin the process of friction ridge identification, additional research is also needed into ridge flow and crease pattern distributions on the hands and feet.
From page 145...
... Examples include bite marks, markings on bullets and cartridge cases, ear prints, lip prints, toolmarks, some bloodstain patterns, and glove prints.39 Although there are general approaches concerning the analytical sequence of various types of impression evidence, each has its own set of characteristics. For example, some types of impression evidence, such as those arising from footwear and tires, require knowledge of manufacturing and wear, while other types, such as ear prints and bloodstain patterns, do not.
From page 146...
... Although some analysis of impression evidence might begin at the scene, the comparison of scene evidence to known exemplars occurs in the laboratory. The educational background of forensic scientists who examine shoeprints and tire track impressions runs the gamut from a high school diploma to scientists with Ph.D.s.
From page 147...
... But there is no defined threshold that must be surpassed, nor are there any studies that associate the number of matching characteristics with the probability that the impressions were made by a common source. It is generally accepted that the specific number of characteristics needed to assign a definite positive identification depends on the quality and quantity of these accidental characteristics and the criteria established by individual laboratories.47 According to Cassidy, many factors and accidental characteristics are required before a positive identification can be established; however, the most important are the examiner's experience, the clarity of the impression, and the uniqueness of the characteristic.48 Proficiency testing for examiners of impression evidence is available through Collaborative Testing Service, Inc., but the proficiency tests for footwear impressions include samples that are either a match or not a match49 -- that is, none of the samples included in the tests have the sort of ambiguities that would lead an experienced examiner to an "inconclusive" 43  Ibid.
From page 148...
... Also, there is no provision or recommendation for proficiency testing or continuing education. SWGTREAD, a group of footwear and tire track examiners formed by the FBI, recommends that a trainee candidate have (1)
From page 149...
... , "match/no match," "responsible for/not responsible for," and "caused with/not caused with."56 Neither the IAI nor SWGTREAD address the statistical evaluation of impression evidence. Summary Assessment The scientific basis for the evaluation of impression evidence is that mass-produced items (e.g., shoes, tires)
From page 150...
... Firearms and toolmark examiners believe that toolmarks may be traced to the physical heterogeneities of an individual tool -- that is, that "individual characteristics" of toolmarks may be uniquely associated with a specific tool or firearm and are reproduced by the use of that tool and only that tool. The manufacture and use of firearms produces an extensive set of 58  SWGTREAD.
From page 151...
... includes images from both cartridge cases and bullets that are associated with crime scenes and is maintained by the ATF. Periodically -- and particularly in the wake of the Washington, DC, 59  Although the metal and initial rifling are very similar, the cutting of the individual barrels, the finishing machining, and the cleaning and polishing begin the process of differentiation of the two sequentially manufactured barrels.
From page 152...
... Similarly, the number of grooves cut into the barrel of a firearm and the direction of "twist" in those grooves are class characteristics that can filter and restrict the range of firearms that match evidence found at a crime scene. "Individual characteristics" are the fine microscopic markings and textures that are said to be unique to an individual tool or firearm.
From page 153...
... 61 indicates that an examiner may offer an opinion that a specific tool or firearm was the source of a specific set of toolmarks or a particular bullet striation pattern when "sufficient agreement" exists in the pattern of two sets of marks. The standards then define agreement as 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 tool marks known to have been produced by the same tool."62 Knowing the extent of agreement in marks made by different tools, and the extent of variation in marks made by the same tool, is a challenging task.
From page 154...
... Journal of Forensic Sciences 52(3)
From page 155...
... And, as was the case for friction ridge analysis and in contrast to the case for DNA analysis, the specific features to be examined and compared between toolmarks cannot be stipulated a priori. But the protocols for DNA analysis do represent a precisely specified, and scientifically justified, series of steps that lead to results with well-characterized confidence limits, and that is the goal for all the methods of forensic science.
From page 156...
... Journal of Forensic Sciences 27(2)
From page 157...
... Journal of Forensic Sciences 19(3)
From page 158...
... Journal of Forensic Sciences 27(2)
From page 159...
... Houck et al. indicate that proficiency testing is conducted regularly for hair experts in crime laboratories.82 Collaborative Testing Services83 offers hair and fiber proficiency tests annually.
From page 160...
... For this reason, cases that might have relied heavily on hair examinations have been subjected more recently to additional analyses using DNA.85 Because of the inherent limitations of hair comparisons and the availability of higher-quality and higher-accuracy analyses based on mtDNA, traditional hair examinations may be presented less often as evidence in the future, although microscopic comparison of physical features will continue to be useful for determining which hairs are sufficiently similar to merit comparisons with DNA analysis and for excluding suspects and assisting in criminal investigations. Summary Assessment No scientifically accepted statistics exist about the frequency with which particular characteristics of hair are distributed in the population.
From page 161...
... The committee found no scientific support for the use of hair comparisons for individualization in the absence of nuclear DNA. Microscopy and mtDNA analysis can be used in tandem and may add to one another's value for classifying a common source, but no studies have been performed specifically to quantify the reliability of their joint use.
From page 162...
... A good overview of fiber evidence is provided by Grieve and Robertson.91 Summary Assessment A group of experienced paint examiners, the Fiber Subgroup of the Scientific Working Group on Materials Analysis (SWGMAT) , has produced guidelines,92 but no set standards, for the number and quality of character other textiles are produced using the same fiber types and color.
From page 163...
... QUESTIONED DOCUMENT EXAMINATION94 Questioned document examination involves the comparison and analysis of documents and printing and writing instruments in order to identify or eliminate persons as the source of the handwriting; to reveal alterations, additions, or deletions; or to identify or eliminate the source of typewriting or other impression marks. Questions about documents arise in business, finance, and civil and criminal trials, and in any matter affected by the integrity of written communications and records.
From page 164...
... Forensic document examination does not involve a study of handwriting that purports to create a personality profile or otherwise analyze or judge the writer's personality or character. Analyses Equipment used in questioned document examination includes microscopes and other optical aids, photographic and other imaging devices, and a wide variety of imaging materials adaptable for use with numerous lighting methods, including those involving ultraviolet, visible, and infrared light, and other regions of the electromagnetic spectrum.
From page 165...
... . The characteristics are further classified into class characteristics (the style that the writer was taught)
From page 166...
... Journal of Forensic Sciences 42(5) :778-786, reports on proficiency tests given to more than 100 questioned document examiners and to a control group of individuals with similar educational backgrounds.
From page 167...
... Painted surfaces are encountered frequently at crime scenes in the form of vehicles, architectural structures, tools, bicycles, boats, and many other items. The results of the examinations often are valuable both during the investigation and as evidence if a trial results.
From page 168...
... Only when physical fitting is possible can an individualized source determination be made Examiners involved with the analysis of paint evidence in the laboratory typically possess an extensive scientific background, because many of the methods and analyses rely heavily on chemistry.101 The suggested minimum education requirement is a bachelor's degree in a natural102,103 or applied science,104 with many candidates possessing a graduate degree. Coursework needs to include one year (or equivalent)
From page 169...
... 2002. Standard guide for using scanning electron microscopy/X-ray spec trometry in forensic paint examinations.
From page 170...
... Journal of the Forensic Sciences Society 8(2-3)
From page 171...
... 115  TWGFEX Recommended Guidelines for Forensic Identification of Intact Explosives. Undated.
From page 172...
... To interpret the results properly, the examiner must have knowledge of the composition of explosives and the reaction products that form when they explode. Interpretation can be further complicated by the presence of contaminants from, for example, the device or soil.116 Examination conclusions for postblast residues range from "the residue present was consistent with an explosive material" to "the residue is only indicative of an explosive" to "no explosive residues were present." TWGFEX recently has developed a set of guidelines for the analysis of postblast explosive residues,117 but has yet to make any recommendations for report wording.
From page 173...
... Although the identification of human remains by their dental characteristics is well established in the forensic science disciplines, there is continuing dispute over the value and scientific validity of comparing and identifying bite marks.120 Many forensic odontologists providing criminal testimony concerning bite marks belong to the American Board of Forensic Odontology (ABFO) , which was organized in 1976 and is recognized by the American Academy of Forensic Sciences as a forensic specialty.
From page 174...
... These features may severely limit the validity of forensic odontology. Also, some practical difficulties, such as distortions in photographs and changes over time in the dentition of suspects, may limit the accuracy of the results.123 Analyses The guidelines of the ABFO for the analysis of bite marks list a large number of methods for analysis, including transillumination of tissue, computer enhancement and/or digitalization of the bite mark or teeth, stereomicroscopy, scanning electron microscopy, video superimposition, and histology.124 The guidelines, however, do not indicate the criteria necessary for using each method to determine whether the bite mark can be related to a person's dentition and with what degree of probability.
From page 175...
... .126 More research is needed to confirm the fundamental basis for the science of bite mark comparison. Although forensic odontologists understand the anatomy of teeth and the mechanics of biting and can retrieve sufficient information from bite marks on skin to assist in criminal investigations and provide testimony at criminal trials, the scientific basis is insufficient to conclude that bite mark comparisons can result in a conclusive match.
From page 176...
... Some of the key areas of dispute include the accuracy of human skin as a reliable registration material for bite marks, the uniqueness of human dentition, the techniques used for analysis, and the role of examiner bias.130 The ABFO has developed guidelines for the analysis of bite marks in an effort to standardize analysis,131 but there is still no general agreement among practicing forensic odontologists about national or international standards for comparison. Although the majority of forensic odontologists are satisfied that bite marks can demonstrate sufficient detail for positive identification,132 no scientific studies support this assessment, and no large population studies have been conducted.
From page 177...
... Bloodstain pattern analysis is employed in crime reconstruction or event reconstruction when a part of the crime scene requires interpretation of these patterns. However, many sources of variability arise with the production of bloodstain patterns, and their interpretation is not nearly as straightforward as the process implies.
From page 178...
... In addition, many bloodstain pattern analysis cases are prosecution driven or defense driven, with targeted requests that can lead to context bias. Summary Assessment Scientific studies support some aspects of bloodstain pattern analysis.
From page 179...
... The uncertainties associated with bloodstain pattern analysis are enormous. AN EMERGING FORENSIC SCIENCE DISCIPLINE: DIGITAL AND MULTIMEDIA ANALYSIS The analysis of digital evidence deals with gathering, processing, and interpreting digital evidence, such as electronic documents, lists of phone numbers and call logs, records of a device's location at a given time, emails, photographs, and more.
From page 180...
... In addition, computers in automobiles that track speed, breaking, and turning are valuable in accident reconstruction. As a result, almost every crime could have digital evidence associated with it.
From page 181...
... A publication of the Department of Justice Computer Crime and Intellectual Property Section, Searching and Seizing Computers and Obtaining Electronic Evidence in Criminal Investigations,141 describes the challenging legal issues surrounding the examination of digital evidence. For example, sometimes the courts have viewed computers as a piece of evidence that is sent to a laboratory for forensic examination, and as having no special legal constraints, while other times, the courts have viewed computers as a virtual room or filing cabinet.142 For the latter cases, a warrant must be 140  See E
From page 182...
... Wide variability exists across forensic science disciplines with regard to techniques, methodologies, reliability, error rates, reporting, underlying research, general acceptability, and the educational background of its practitioners. Some of the forensic science disciplines are laboratory based (e.g., nuclear and mitochondrial DNA analysis, toxicology, and drug analysis)


This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More information on Chapter Skim is available.