Forensic Analysis Weighing Bullet Lead Evidence (2004) / Chapter Skim
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4. Interpretation
4. Interpretation
Pages 71-108
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From page 71... ...
This chapter is split into two sections: "Significance of the Bullet Manufacturing Process" and "Compositional Analysis of Bullet Lead as Evidence in the Legal System." SIGNIFICANCE OF THE BULLET MANUFACTURING PROCESS The following description of the processes leading to the production of loaded ammunition represents the bullet manufacturing practices currently in place at large-scale producers in the United States. (Processes used overseas are less well documented.)
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D Introduction to the Bullet Manufacturing Process: Committee on Scientific Assessment of Bullet Lead Elemental Composition Comparison, Washington, DC February 3, 2003.
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for bullet lead processing in large pots.8 The designation of primary smelter is reserved for manufacturing facilities that produce lead from ores. Such facilities are rarely associated directly with bullet production in the United States, but this is not the case in some foreign countries.
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D Introduction to the Bullet Manufacturing Process: Committee on Scientific Assessment of Bullet Lead Elemental Composition Comparison, Washington, DC February 3, 2003.
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D Introduction to the Bullet Manufacturing Process: Committee on Scientific Assessment of Bullet Lead Elemental Composition Comparison, Washington, DC February 3, 2003.
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DETAILS OF BULLET PRODUCTION This section details the venous stages leading to the production and distnbution of boxes of loaded ammunition. Comments on the variations that are known to exist at venous stages are given here, but their implications for the homogeneity of melts, billets, wires, and so on, are discussed in the section titled "Compositional Information." Sources and Use of Lead With over 3.5 billion pounds of lead smelted each year in the Unites States, the 85-118 million pounds used in bullet manufacturing comprises about 2.53 percent of total lead use; lead-acid storage batteries probably represent the largest products 17 Secondary smelters that produce bullet lead are also geni5Commercial reloaders are often known as remanufacturers.
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Compilation of Air Pollutant Emission Factors, AP-42, Fifth Edition, Volume I: Stationary Point and Area Sc=ources, Secondary Lead Chapter 12 section 11. Research Triangle Park, NC, January 1995.
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Table 4.4 shows an example of one manufacturer's compositional requirements for lead to be used in .22 long rifle bullets. Some bullet producers use asreceived billets from secondary smelters, and others conduct tertiary melting to make additional adjustments to the lead composition or to recycle scraps of lead produced during bullet production.
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Thus, it can be reasonably assumed that the rate of compositional change even when molten lead batches are mixed during a pour from one poured ingot to the next poured ingot is much smaller than the measurement precision available. It also follows that any compositional change in the lead initially poured into an ingot (or billet)
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In other instances, the lead ingots, pigs, or billets are shipped to bullet manufacturers, and the bullet manufacturers may use the billets directly in their extruders to produce wire. There are also instances in which the ingots or pigs obtained from the secondary smelters are remelted to pour new billets at the bullet manufacturing plant.
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D Introduction to the Bullet Manufacturing Process: Committee on Scientific Assessment of Bullet Lead Elemental Composition Comparison, Washington, DC February 3, 2003.
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COMPOSITIONAL INFORMATION Multiple steps are required to move from bullet production to boxes of ammunition, and manufacturers vary in their processing of materials leading to bullet formation. In addition, storage times before actual packaging and shipping depend heavily on caliber; for example, high-production munitions, such as .22 caliber, probably move more rapidly from slug production to shipping than less-common munitions.
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· Mixing of Slugs, Bullets, and Loaded Ammunition. Some manufacturers 44Koons, R
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in ammunition production. The loaded ammunition can be routed directly to a packaging area, in which case no additional mixing occurs.
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The ramifications of identifying bullets whose compositions are analytically indistinguishable and their possible association with a single CIVL are discussed later in this chapter. COMPOSITIONAL ANALYSIS OF BULLET LEAD AS EVIDENCE IN THE LEGAL SYSTEM This section discusses the legal aspects of CABL evidence.
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Berger, The Supreme Court's Trilogy on the Admissibility of Expert Testimony, in Federal Judicial Center, Reference Manual on Scientific Evidence 9 (2d ed.
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. In Kumho, the Court extended Daubert's reliability requirement to nonscientific expert testimony under Rule 702: "Daubers's general holding setting forth the trial judge's general 'gatekeeping' obligation applies not only to testimony based on 'scientific' knowledge, but also to testimony based on 'technical' and 'other specialized' knowledge." Id.
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Imwinkelried, Scientific Evidence § 1-13 (3d ed.
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be more probable or less probable with the evidence than without the evidence.72 Rule 402 makes relevant evidence admissible in the absence of a rule of exclusion, and Rule 403 specifies circumstances under which a trial court is permitted to exclude relevant evidence. Rule 403 reads: "Although relevant, evidence may be excluded if its probative value is substantially outweighed by the danger of unfair prejudice, confusion of the issues, or misleading the jury, or by considerations of undue delay, waste of time, or needless presentation of cumulative evidence." In Daubert, the Supreme Court noted that "expert evi70E.g., People v.
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. 76As the committee was completing its report, a federal district court excluded CABL evidence under the Daubert standard.
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The lead material in one bullet and one projectile was analytically indistinguishable, as was the lead in one bullet and the other two projectiles.")
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1996) ("An expert testified that such a finding is rare and that the bullets must have come from the same box or from another box that would have been made by the same company on the same day."; the court wrote that "expert testimony demonstrated a high probability that the bullets spent at the first robbery and the last robbery originated from the same box of cartridges.")
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A 2002 FBI publication states the conclusion as follows: "Therefore, they likely onginated from the same manufacturer's source (melt) of lead."93 Testimony to the same effect has also been proffered.94 Recent laboratory reports reviewed by the committee contain the following conclusion: "The specimens within a composition group are analytically indistinguishable.
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1997) : Beyond the inherent problems with the expert testimony itself, we are also persuaded that the prosecutor's "snowflake or fingerprint" comment during closing must necessarily have further misled the jury in its task of assessing the probative value of Peters' identical-composition testimony.
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1997) ("To begin with, we have no doubt that ICP analysis of lead bullets is a process adequately accepted by the scientific community and producing sufficiently reliable results to warrant the admission of expert testimony regarding the test and the test results.")
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is 0.90, and the probability of a match by coincidence or error of two bullets from different CIVLs (the false positive probability) is 1 in 500 or 0.002 The likelihood rations would then be 0.90/0.002 = 450.
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In this context, the posterior odds given the evidence are the odds that the two bullets came from the same melt given that they are analytically indistinguishable ("match") ; the prior odds are the odds that the bullets came from the same melt based on the other evidence in the case (such as evidence indicating that the bullets may have come from the defendant's supply)
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False positives occur when a laboratory error or a coincidence (two CIVLs with analytically indistinguishable composition) causes two bullets to match.
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the 2-SD overlap and range overlap method used by the FBI for declaring a match do not have quantifiable error rates (although approximate error rates can be calculated as in Chapter 3~; and (3) the FBI study has been neither peer-reviewed nor published.ll5 Daubert/Kumho Factors The Daubert/Kumho factors previously referred to provide an indication of whether proposed expert testimony is sufficiently reliable to be admissible at trial.
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ii7Like many forensic techniques, CABL evidence gained admissibility before the demanding standards of Daubert were operative. The FBI has attempted to satisfy these standards through its recent publications and by referring the issue to this committee.
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The fact that courts have generally admitted this testimony is not the equivalent of scientific acceptance, owing to the paucity of published data, the lack of independent research, and the fact that defense lawyers have generally not challenged the technique.~23 The fact that the specifically mentioned Daubert factors are not fully satisfied does not mean that CABL evidence should not be admitted under the reliability standards of Rule 702. In Kumho Tire, the Court concluded "that a trial court may consider one or more of the more specific factors that Daubert mentioned when doing so will help determine that testimony' s reliability.
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1995) ("This box of 50 cartridges contained the same loading code, 2TB9OL, as the empty cartridge box found in the snowbank at the scene of Freeman's arrest.
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If multiple compositions present in the crime-scene lead are analytically indistinguishable from lead groups in partial boxes of ammunition, it is much more likely that the crime-scene bullets came from those boxes than it is when only one compositional group is present.")
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on CABL evidence are discoverable, it is more logical and of greater use to include these data in the laboratory report. i32Opponents of liberal discovery argue that criminal discovery will encourage perjury, lead to the intimidation of witnesses, and, because of the Fifth Amendment, be a one-way street.
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The summary must describe the witnesses' opinions, the bases of and reasons for the opinions, and the witnesses' qualifications. This provision was intended to "expand federal criminal discovery" in order to "minimize surprise that often results from unexpected expert testimony, reduce the need for continuances, and to provide the opponent with a fair opportunity to test the merit of the expert's testimony through focused crossexamination."~38 Although the ABA Standards recommend this type of discovery,~39 most states do not have comparable provisions.
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Recommendation: Expert witnesses should define the range of "compositionally indistinguishable volumes of lead" (CIVL) that could make up the source of analytically indistinguishable bullets, because of variability in the bullet manufacturing process.
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An examiner may also testify that having CABL evidence that two bullets are analytically indistinguishable increases the probability that two bullets came from the same CIVL, versus no evidence of match status. Recommendation: Interpretation and testimony of examiners should be limited as described above and assessed regularly.
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Moreover, a section of the laboratory report translating the technical conclusions into language that a jury could understand would greatly facilitate the proper use of this evidence in the cnm~nal justice system.~47 Finally, measurement data (means and standard deviations) for all of the crime scene bullets and those deemed to match should be included.
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