4
Interpretation

The primary objective of compositional analysis of bullet lead (CABL) is to produce evidence for use in court. Although the evidence is analyzed with scientific instrumentation and statistical methods, its presentation and use in court are subject to human interpretation and error. Attorneys, judges, juries, and even expert witnesses can easily and inadvertently misunderstand and misrepresent the analysis of the evidence and its importance. It is therefore essential to discuss whether and how the evidence can be used. It is first necessary to introduce the lead and bullet manufacturing processes so that the implications of bullet production for the legal system are fully understood. 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.) As shown in this chapter, the processes vary at numerous points, depending on such factors as the manufacturer, the caliber and style of bullet, the magnitude of a production run (which is often dictated by the demand for a particular caliber), and the size of the manufacturing facility. This



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence 4 Interpretation The primary objective of compositional analysis of bullet lead (CABL) is to produce evidence for use in court. Although the evidence is analyzed with scientific instrumentation and statistical methods, its presentation and use in court are subject to human interpretation and error. Attorneys, judges, juries, and even expert witnesses can easily and inadvertently misunderstand and misrepresent the analysis of the evidence and its importance. It is therefore essential to discuss whether and how the evidence can be used. It is first necessary to introduce the lead and bullet manufacturing processes so that the implications of bullet production for the legal system are fully understood. 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.) As shown in this chapter, the processes vary at numerous points, depending on such factors as the manufacturer, the caliber and style of bullet, the magnitude of a production run (which is often dictated by the demand for a particular caliber), and the size of the manufacturing facility. This

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence section details procedures that are believed to account for the manufacturing processes used for .22 caliber rimfire and other bullets by major producers in the United States. (This process is described because .22 caliber rimfire ammunition is one of the most popular ammunition rounds produced.) It has been estimated that 50–75 percent of all ammunition sold in the United States originates with U.S. manufacturers and that about 50 percent of ammunition used by the U.S. military (for example, 9-mm, 7.62-NATO, and 5.56-NATO ammunition) and more than 50 percent of non-U.S. issue military calibers (such as 7.62 × 39 <AK-47> and British .303 <Enfield>) are imported.1, 2, 3 GENERAL INFORMATION ON BULLETS On the order of 85–118 million pounds of lead is used each year in the production of bullets4 in the United States.5, 6 The exact number of each caliber and type of bullet (such as jacketed or hollow point) is not known, but some estimates of production volumes have been provided by the Sporting Arms and Ammunition Manufacturers’ Institute7 and are shown in Table 4.1. It is generally acknowledged that .22 caliber bullets are the dominant type sold. Table 4.2 provides some examples of typical bullet masses for various calibers. Using 70 grains (0.16 oz, 4.54 g) as an arbitrarily assumed average bullet mass allows the estimation that the 85–118 million pounds of bullet lead produces about 8.5–11.8 billion bullets per year in the United States. OVERVIEW OF BULLET PRODUCTION Figure 4.1 is a simplified flow chart for bullet production and approximate mass of material involved in each of the processed materials. Table 4.3 has been prepared from the general information given in Figure 4.1 to illustrate the approximate number of bullets associated with each of the manufacturing steps or 1   Greenberg, R. R. March 3, 2003. Verbal communication to committee after visiting the SHOT Show February 13–16, 2003. 2   Shotgun News Special Interest Publications, Peoria, IL May 20, 2003. A collection of firearms related advertisements for retailers and wholesalers. 3   CABL also has value for the matching of foreign-produced bullet lead; this value varies according to the lead’s nation of origin and that nation’s lead recycling and manufacturing processes. The analysis of foreign-produced bullets is not discussed in detail in this report. 4   The committee assumes these numbers include lead for shot as well as bullets. 5   Biviano, M. B.; Sullivan, D. E.; Wagner, L. A. Total Materials Consumption: An Estimation Methodology and Example Using Lead—A Materials Flow Analysis. USGS Circular: 1183. April, 1999. <http://pubs.usgs.gov/circ/1999/c1183>. 6   Smith, G. R. USGS Minerals Yearbook 2001: Lead. Reston, VA 2001. <http://minerals.er.usgs.gov/minerals/pubs/commodity/lead/leadmyb01.pdf>. 7   Green, K. D. Introduction to the Bullet Manufacturing Process: Committee on Scientific Assessment of Bullet Lead Elemental Composition Comparison, Washington, DC February 3, 2003.

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence TABLE 4.1 Annual Production of Ammunitions Produced in the United States Ammunition Type No. Rounds Produced per Year, billions No. Boxes Produced per Year, millions No. Units per Box Shotgun shells (all gauges) 1.1 44 25 Rifle, center fire 0.25 12.5 20 Pistol and revolver, center fire 0.55 11 50 Rifle and pistol, rimfire 2 40 50   Source: See Footnote 7. TABLE 4.2 Examples of Various Caliber and Style of Bullets and Estimated Bullet Mass Caliber Style Total Mass of Projectile (Mass of Pb if Jacketed) Grains Ounces Grams .22 Long rifle Round nose/Hollow point 40 0.0914 2.59 9 × 19 mm Lead round nose 124 0.283 8.04 9 × 19 mm Full metal jacket 124 (103.0) 0.283 (0.237) 8.04 (6.71) .38 special Lead round nose 150 0.343 9.72 44 Remington magnum Lead truncated cone 240 0.549 15.6 5.56 × 45 mm Full metal jacket 62 (31.6) 0.142 (0.0722) 4.02 (2.05) 5.56 × 45 mm Full metal jacket 55 (46.1) 0.126 (0.105) 3.56 (2.99) 7.62 × 51 mm Full metal jacket 145 (93.1) 0.331 (0.213) 9.40 (6.03) products. Calculations assumed a mass of 40 grains (0.0914 oz, 2.59 g) for a .22 rimfire projectile. The number of projectiles is based on 100 percent yield. Since some material is not converted directly to the final bullets (for example, initial piece of extruded wire, weep from bullet presses), the actual number of projectiles produced will be lower. In the United States, secondary smelters melt recycled lead (primarily from recycled lead-acid storage batteries) 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. Secondary smelting is reported to account for half the lead produced in the 8   Smith, G. R. Lead Recycling in the United States in 1998. USGS Circular: 1196-F. 2002. <http://pubs.usgs.gov/circ/c1196f/>.

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence FIGURE 4.1 Flow diagram of bullet materials, a general description of the many steps involved in bullet production. TABLE 4.3 Approximate Masses and Numbers of Bullets Produced from “Single Unit” of Various Stages in Manufacturing Processa Source of Material Weight of Material (lbs) Mass of Material (kg) Yield (of .22 Caliber Bullets) Melt pot 200,000 90,719 35,000,000 Melt pot 100,000 45,360 17,500,000 Sow 2,000 907 350,000 Billet 70–350 32–159 12,250–61,250 Pig/Ingot 60–125 27–57 10,500–21,875 aGreen, K. D. Introduction to the Bullet Manufacturing Process: Committee on Scientific Assessment of Bullet Lead Elemental Composition Comparison, Washington, DC February 3, 2003.

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence United States. There are 50 plants, with capacities ranging from 1,000 to 120,000 tons/year.9 Refining of the melt to remove various elements present either as impurities or as previously added alloy elements can occur at the secondary smelter.10, 11 After refinement, Sb, less frequently Sn, and sometimes both elements may be added to harden the bullet. Finally, the melt is poured into various smaller products, including billets, which are sent to the bullet manufacturer. The bullet manufacturer may use the purchased billets directly for production, but it is not uncommon for bullet manufacturers to remelt the purchased lead and cast their own billets for production.12 The bullet manufacturer extrudes bullet wire from a solid billet; this results in one or more wires per billet, depending on whether the extruder die has one or more extrusion ports. Generally, a continuous wire is not produced from multiple billets due to the likelihood of discontinuity and the production of a flawed slug at the junction due to lead lamination. The size of the extruded wire is dictated by the caliber (diameter) of the bullet to be produced from that wire. The bullet wire is then fed into a machine that cuts it to predetermined lengths to generate slugs of the approximate weight and dimensions of the final bullet. The slugs are collected in bins, whose size varies from plant to plant. In larger manufacturing facilities, several extruders may be operated in parallel in the production of slugs of a given caliber, and the slugs from the various extruders may be collected in the same bin. A given wire is converted to slugs of a given length and diameter. The slugs are then pressed into the final shape of the bullet, a jacket is applied (if appropriate), and the bullets are again collected in bins.13 The bullets are seated into appropriately prepared cartridge cases (loaded with primer and powder) to form the loaded ammunition, which is either collected in bins or sent directly to machinery for packing in boxes. The boxes generally contain 20–50 rounds each, depending on the caliber and the products being offered by the company. A more specific example of the wire-to-ammunition production steps for .22 caliber rimfire bullet production is as follows:14 9   U.S. Environmental Protection Agency. Compilation of Air Pollutant Emission Factors, AP-42, Fifth Edition, Volume I: Stationary Point and Area Scources, Secondary Lead Chapter 12 section 11. Research Triangle Park, NC, January 1995. 10   Randich, E.; Duerfeldt, W.; McLendon, W.; and Tobin, W. Foren. Sci. Int. 2002, 127, 174–191. 11   Frost, G. E. Ammunition Making, Chapter 3. National Rifle Association of America, Washington, DC 1990, 25–43. 12   Green, K. D. Introduction to the Bullet Manufacturing Process: Committee on Scientific Assessment of Bullet Lead Elemental Composition Comparison, Washington, DC February 3, 2003. 13   Bullet cores are extruded as wires of a slightly smaller diameter than for unjacketed bullets of the same caliber, are cut into slugs, and are swaged into thimble-like jackets. The production of bullet cores is otherwise identical to the production of bullets. 14   Green, K. D. Introduction to the Bullet Manufacturing Process: Committee on Scientific Assessment of Bullet Lead Elemental Composition Comparison, Washington, DC February 3, 2003.

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence Pinch cut to partially perforate the wire. Tumble the partially perforated wire to break it into slugs. Swage press to final shape (three steps are needed). Wash and rinse. Flash plate with copper alloy (if high-velocity product is being made). Lubricate. Assemble into loaded ammunition. Pack ammunition in boxes. The boxes are then generally bundled into appropriately sized shipping quantities—such as cartons, crates, or pallets—and sent to jobbers, distributors, wholesalers, or large retailers. They then go to the retailer’s shelf for purchase by the consumer. Reloaders, both commercial and private, are another source of loaded ammunition and are less directly connected to large-volume manufacturers.15 Using refurbished cases for reloading, reloaders make less-expensive ammunition. In some instances, reloaded bullets are made from melted scrap lead, such as discarded wheel-balancing weights that are remelted and poured into bullet molds. DETAILS OF BULLET PRODUCTION This section details the various stages leading to the production and distribution of boxes of loaded ammunition. Comments on the variations that are known to exist at various 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 2.5–3 percent of total lead use; lead-acid storage batteries probably represent the largest product.16, 17 Secondary smelters that produce bullet lead are also gen- 15   Commercial reloaders are often known as remanufacturers. The concentrations of elements in component bullets used by reloaders are similar to the concentrations in bullet lead used by major manufacturers. Component bullet unit sales are a small fraction (5–10 percent) of loaded ammunition sales, but can follow wider distribution channels because there are fewer shipping restrictions. Reloaded ammunition is not expected to comprise a large percentage of the ammunition involved in casework. 16   Biviano, M. B.; Sullivan, D. E.; Wagner, L. A. Total Materials Consumption: An Estimation Methodology and Example Using Lead—A Materials Flow Analysis. USGS Circular: 1183. April, 1999. <http://pubs.usgs.gov/circ/1999/c1183>. 17   Smith, G. R. USGS Minerals Yearbook 2001: Lead. Reston, VA 2001. <http://minerals.er.usgs.gov/minerals/pubs/commodity/lead/leadmyb01.pdf>.

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence erally involved in the production of “battery lead.” Chemical compositional requirements for bullet lead are much less stringent (that is, they have less-restrictive tolerances) than are needed for battery lead. However, a hardened lead is generally needed for bullets.18, 19 Hardening is typically accomplished by the addition of Sb to the melt. Sn can also be used, but it is more expensive. Other components of bullet lead are generally carried over from the lead source, and maximal tolerances in their concentrations are normally specified by the bullet manufacturer. Bullets are reportedly produced mainly from recycled lead in the United States. Therefore, it is impossible to trace bullet lead back to the original source of the ore,20 and no detailed discussion will be presented here on the primary smelters and ore processing except to note that the ores are sulfides and contain small amounts of Cu, Fe, Zn, precious metals, and other trace and minor elements, such as As, Sb, and Bi. The primary smelting process involves removal of those elements by reduction and refining. Secondary Lead Smelters As noted previously, the dominant source of bullet lead is the electrode materials from recycled batteries. The melting process takes place in pots that may contain, for example, 50–350 tons of melt. The descriptions given below are typical; they might not be applicable to all smelters. The first step in secondary lead refining is treatment of scrap to remove metallic and nonmetallic contaminants. That is done by mechanical breaking and crushing to separate extraneous contaminants and then “sweating” the separated lead scrap in a reverberatory furnace to isolate the lead from metals that have higher melting points. The next step is smelting in a blast furnace to make “hard” (high-Sb) lead or in a reverberatory furnace to make “semisoft” (3–4 percent Sb) lead. Refining is normally done in a batch process that takes a few hours to a few days in kettle-type furnaces that have production capacities of 25–150 tons/day.21 In the refining process, Cu, Sb, As, and Ni are the main elements removed. It is generally assumed that Sb is the element whose content is most critical because it determines the bullet hardness.22, 23 18   Randich, E.; Duerfeldt, W.; McLendon, W.; and Tobin, W. Foren. Sci. Int. 2002, 127, 174–191. 19   Peters, C.; Havekost, D. G.; Koons, R. D. Crime Lab. Digest 1988, 15(2), 33–38. 20   Smith, G. R. USGS Minerals Yearbook 2001: Lead. Reston, VA 2001. <http://minerals.er.usgs.gov/minerals/pubs/commodity/lead/leadmyb01.pdf>. 21   U.S. Environmental Protection Agency. 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. 22   Randich, E.; Duerfeldt, W.; McLendon, W.; and Tobin, W. Foren. Sci. Int. 2002, 127, 174–191. 23   Peters, C.; Havekost, D. G.; and Koons, R. D. Crime Lab. Digest 1988, 15(2), 33–38.

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence TABLE 4.4 Example of Manufacturer’s Compositional Requirements for Pb to Be Used in .22 Long Rifle Projectilesa Preferred Analysis Weight Percent Sb 0.85 ± 0.15 % Maximal Impurities Weight Percent Al 0.001% As 0.05–0.10% Bi 0.05% Cd 0.001% Cu 0.03% Ca 0.001% Fe 0.001% Ni 0.001% Se 0.002% Ag 0.01% S 0.001% Te 0.01% Sn 0.15–0.2% Zn 0.001% Sow Size Weight in Pounds Maximum 2,200 lb Minimum 1,500 lb aPrengaman, R. D. Lead and Lead Refining: Committee on Scientific Assessment of Bullet Lead Elemental Composition Comparison, Washington, DC March 3, 2003. In the production of bullet lead, the manufacturer generally has requirements for the concentrations of the final lead alloy.24 The elemental compositional requirements can vary with the bullet manufacturer. Depending on the element, either maximal allowable or ranges of concentrations may be specified. 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 as-received 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. A secondary smelter may produce solid lead of various shapes, including ingots, pigs, and billets. An analysis certificate accompanies the product shipped to the bullet manufacturer; it uses a smelter-dependent format that contains various degrees of analytical detail. Spark-emission optical spectroscopy is the technique generally used for analysis of the alloy at the smelters.25 The technique 24   Prengaman, R. D. Lead and Lead Refining: Committee on Scientific Assessment of Bullet Lead Elemental Composition Comparison, Washington, DC March 3, 2003. 25   Prengaman, R. D. Lead and Lead Refining: Committee on Scientific Assessment of Bullet Lead Elemental Composition Comparison, Washington, DC March 3, 2003.

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence generally produces precision on the order of ±10–20%; however, when the most stringent standardization procedures are implemented, precision may approach ±5 percent.26 There is no requirement by the bullet manufacturers that all lead ingots received from a smelter come from a single pour or melt. It is generally assumed that the composition of a given melt is constant and homogeneous from the beginning to the end of the pour if nothing is added to the pot during the pour.27 The assumption of homogeneity is based on the convective mixing in the vat and the relatively short pouring time. It should be noted that during a pour material may be added to the original melt, thus producing time-varying compositional changes. The additions may include bulk material (ingots, pigs, and so on), manufacturing scrap (pieces of bullet wire, scrap from bullet-forming operations, and the like), or molten lead introduced from a secondary vat. Examples of the time-dependent variation in composition can be seen in some of the data of Koons and Grant.28 In the case of at least one manufacturer, billets are not poured from a vat that has a constant composition; instead, while the vat is being poured, molten lead from another pot is continuously added to maintain the level of molten lead in the vat being poured. Thus, compositional changes can occur during casting. The data of Koons and Grant29 indicate that compositional change occurs over several 60 lb ingots that were being poured. For example, the concentration of Sn decreased by 60 percent (from 0.030 to 0.012 percent Sn) over a 30 minute period, the largest change of the data presented. Combining this information with the standard deviations for the analytical measurement (that is, < 0.001 percent Sn) it can be estimated that approximately 15 ingots (approximately 850 lbs of Pb) were poured before the average concentrations changed by one standard deviation. 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) would be indistinguishable from the molten lead added to the mold to complete the pour of that ingot, as long as the casting of the ingot was completed in a single pour. Randich et al.30 also showed occasional distinct concentration changes in some elements as samples were extracted from the beginning, middle, and end of the pour. Statistical analysis of the changes showed that there was no distinct time-dependent one-directional change (that is, always increasing or decreasing 26   Mitteldorf, A. J. In Trace Analysis; Morrison, G. H., Ed.; John Wiley and Sons: New York, 1965, pp 193–243. 27   Prengaman, R. D. Lead and Lead Refining: Committee on Scientific Assessment of Bullet Lead Elemental Composition Comparison, Washington, DC March 3, 2003. 28   Koons, R. D. and Grant, D. M. J. Foren. Sci. 2002, 47, 950–958. 29   Koons, R. D. and Grant, D. M. J. Foren. Sci. 2002, 47, 950–958. 30   Randich, E.; Duerfeldt, W.; McLendon, W.; and Tobin, W. Foren. Sci. Int. 2002, 127, 174–191.

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence as the pour proceeded), which would suggest for these data that lead of a different composition was being added during the pour, rather than that some chemical process occurred that depleted or enriched a given element as a function of time. The former possibility (the addition of lead during the pour) is supported by the data of Koons and Grant,31 who presented a more detailed analysis of billets resulting from pours. Koons and Grant used several of the same data sets as Randich et al.32 Billet Production Billets weigh 70–350 lbs (32–159 kg), depending on the manufacturer and the size and type of extruder that is used in the production of bullet wire.33, 34 In some instances, the secondary smelter is also a bullet manufacturer, and the billets produced are used on site in the production of wire, slugs, and so forth. 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. Various activities can occur during this tertiary melting that affect the final billet composition. For example, melted lead prior to casting in billets is typically “fluxed” to remove oxidized lead metal elements and other impurities. The fluxing agent can contain a number of different materials, and is often borate-based in commercial bullet manufacturing operations. Nitrogen gas is also a common fluxing agent. The flux entrains the impurities and floats them to the surface of the lead melt for removal. Bullet Production Billets are used without alteration (in their original, solid state) in the extruders to produce bullet wire. The mass of the wire is somewhat less than the mass of the billet, because the tail end of the billet cannot be forced through the extrusion die by the ram.35, 36 The length of the wire is governed by the billet 31   Koons, R. D. and Grant, D. M. J. Foren. Sci. 2002, 47, 950–958. 32   Randich, E.; Duerfeldt, W.; McLendon, W.; and Tobin, W. Foren. Sci. Int. 2002, 127, 174–191. 33   Green, K. D. Introduction to the Bullet Manufacturing Process: Committee on Scientific Assessment of Bullet Lead Elemental Composition Comparison, Washington, DC February 3, 2003. 34   Prengaman, R. D. Lead and Lead Refining: Committee on Scientific Assessment of Bullet Lead Elemental Composition Comparison, Washington, DC March 3, 2003. 35   Green, K. D. Introduction to the Bullet Manufacturing Process: Committee on Scientific Assessment of Bullet Lead Elemental Composition Comparison, Washington, DC February 3, 2003. 36   Prengaman, R. D. Lead and Lead Refining: Committee on Scientific Assessment of Bullet Lead Elemental Composition Comparison, Washington, DC March 3, 2003.

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence size and the wire diameter (bullet caliber). For example, a 70-lb billet should produce about 114 ft of wire intended for .22 caliber ammunition, but the same billet should produce about 27 ft of wire if .45 caliber bullets are the intended product. The extruder die may have a single exit port that produces a single wire strand from the billet, or it may have multiple extrusion ports that produce several wires from a single billet. Several feet of the wire formed at the beginning of the extrusion process may be discarded and recycled into a future billet.37 In brief, the wire is used as feed for a cutter, which consists of a machine that automatically introduces the wire into a cutting device to produce slugs, small cylinders of lead whose length and mass are close to those of the final bullet. The slugs are stored in large bins that may hold substantial quantities of slugs from different wires. The binned slugs are fed into hoppers that feed the presses that form the bullets. Although it is not a true swaging process, this term is commonly encountered in the literature describing the process. Thus formed, the bullets are then tumbled, sometimes lubricated, and stored in bins.38, 39 For some bullet types, a metal jacket is added. Production of Loaded Ammunition The loaded ammunition, which is sometimes referred to as rounds or cartridges, consists of a brass case that is charged with primer and powder and into which the bullet is pressed. Bullets and cases from bins are fed into hoppers, and the process of ammunition production proceeds in an automated fabrication machine. The product is sent directly to the packaging operation or is placed in large bins for later packaging.40, 41 Packaging and Distribution The bullet manufacturer packages the ammunition in boxes for shipment. The box typically is labeled with a stamp that refers to the “boxing lot,” which may be recorded as a date or simply a number. In some manufacturing plants, 37   Frost, G. E. Ammunition Making, Chapter 3. National Rifle Association of America, Washington, DC 1990, 25–43. 38   Frost, G. E. Ammunition Making, Chapter 3. National Rifle Association of America, Washington, DC 1990, 25–43. 39   In some cases, bullets may be washed, rinsed, and plated in addition to being tumbled and lubricated. Each step can introduce further mixing of bullets from different lead wires and discrete sections of lead wire. 40   Green, K. D. Introduction to the Bullet Manufacturing Process: Committee on Scientific Assessment of Bullet Lead Elemental Composition Comparison, Washington, DC February 3, 2003. 41   Frost, G. E. Ammunition Making, Chapter 3. National Rifle Association of America, Washington, DC 1990, 25–43.

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence • Homogeneity within CIVLs. FBI expert witnesses frequently imply or state in their testimony that if bullets came from the same melt,112 they will always match, that is, the test has perfect sensitivity. A single study by FBI personnel tested the assumption of homogeneity of melts and found it to be reasonable (sensitivity more than 90 percent).113 A study by critics of the assumption (Randich et al.) concludes that lead from a single melt can be inhomogeneous.114 Possible reasons for this conclusion were discussed. However, no measure of sensitivity is given in the study, and the authors did not publish the standard deviations of their measurements, so it cannot be determined to what extent the differences found were analytically indistinguishable. Despite the debate, the existence of inhomogeneity in a melt should not seriously affect the probative value of the evidence and may, in some respects, enhance it. We discuss the reason for this below. Even if there is considerable inhomogeneity in a melt, two bullets that come from one melt and that have the same composition must have come from a subpart of the melt that was homogeneous. Fewer bullets can be made from a subpart than from the whole melt, so the fact of inhomogeneity within a melt, if it exists, does not weaken the inferences that can be legitimately made about matching bullets. However, because the degree of inhomogeneity will in general not be known, it must be assumed, conservatively, that the number of bullets of the same composition is such as would be produced from an entire melt. The principal risk of inhomogeneity is a false negative—two bullets declared not to match when they come from the same melt. Under our system of justice, such errors are less objectionable than false positives because they would usually favor a suspect. The committee has addressed the issue of homogeneity by defining a source not as a melt, but rather as a CIVL (compositionally indistinguishable volume of lead), which may be limited to a subpart of a melt. • False Positives. False positives occur when a laboratory error or a coincidence (two CIVLs with analytically indistinguishable composition) causes two bullets to match. The rate of laboratory error is unknown because the FBI Laboratory does not have a program of testing by an external agency that has been designed to assess the proficiency of its examiners. The FBI’s internal testing program does not appear to be designed to determine an error rate. If we 112   In this case the term “melt” is used rather than CIVL because that is the term used by the FBI in their testimony. “Melt” will also be used on other occasions in this chapter when the original source uses the term. 113   Robert D. Koons and Diana M. Grant, Compositional Variation in Bullet Lead Manufacture, 47 J. Forensic Sci. 950 (2002) (of 456 comparisons of bullets from common sources, differences were statistically and analytically significant in only 33). 114   Erik Randich et al., A Metallurgical Review of the Interpretation of Bullet Lead Compositional Analysis, 127 Forensic Sci. Int’l 174 (2002).

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence assume the laboratory’s error rate is in fact low (an assumption not currently grounded in evidence and made here only for the sake of the argument at hand), then the overwhelming contribution to the denominator of the likelihood ratio is CIVLs that are coincidentally identical in their composition. The frequency of coincidentally identical CIVLs is unknown. Based on available data, the frequency of coincidental matches has been studied by the FBI. The data used in the FBI study have been further analyzed by the committee as described in Chapter 3. Those analyses have found some evidence supporting the assumption that the frequency of coincidental false positives is quite low. However, the FBI’s study is weakened because (1) the data used by the FBI were culled by the Bureau from a larger data set consisting of a collection of bullets analyzed by the FBI over a period of 14 years, and the method of culling may have introduced statistical bias; (2) 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.115 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. They expressly apply to the federal courts, to the state courts in those states that have adopted Daubert, and are likely to be influential to some degree in those states retaining the Frye standard. We briefly examine below the assumptions of homogeneity and low false positive error rates from this perspective.116 • Whether the theory can be and has been tested. Both homogeneity and a low false positive rate are assumptions that can be and have been tested, as described above and in Chapter 3. As noted in those discussions, the tests of both assumptions have weaknesses. For the reasons stated above, the assumption of homogeneity within a melt is not crucial to the value of the evidence. The 115   The authors of the Randich study claim in conclusory fashion that the rate of false positives is high but do not calculate a rate. If their data and assertions are accepted, the rate for their Table 3 would be about 1 in 500. The difference between the FBI rate and the Randich rate may be due in part to the fact that the Randich data are from only two manufacturers whereas the FBI data are from all manufacturers and cover a much longer period. 116   One federal court of appeals has admitted CABL evidence under the Daubert test. United States v. Davis, 103 F.3d 660 (8th Cir. 1996). However, the court did not have the information that the committee had available to it. Moreover, the court overstated the probative value of the evidence. The court wrote: “The evidence made it more probable than not that the expended bullets originated from the cartridge box found in the Nissan.” Id. at 674. As the committee was completing its report, a federal district court excluded CABL evidence under the Daubert standard. United States v. Mikos, 2003 WL 22922197, No. 02 CR 137 (N.D. Ill. Dec. 9, 2003).

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence assumption of a low false positive rate is important. As the analysis in Chapter 3 indicates, the statistical method used by the FBI may be leading to a false positive rate much higher than that assumed by examiners. A statistical method can be chosen to minimize the false positive rate, but this is always done at the expense of a higher false negative rate. Additional testing would be needed to fully satisfy the Daubert/Kumho testing requirement. • Whether the theory has been subjected to peer review and publication. There are very few peer-reviewed articles on homogeneity and the rate of false positive matches in bullet lead composition.117 Early articles focused on NAA118 and other techniques,119 used fewer elements in the analysis, and did not address the question of statistical interpretation. Moreover, some of the published articles appeared in FBI publications.120 Outside reviews have only recently been published.121 Because this evidence is less than conclusive and the case volume that utilizes this technique is low, the subject has not received the broad review that DNA testing and some other techniques have. Again, more such work would be needed to provide a strong basis for this admissibility factor. • Whether the theory has a known error rate. The false positive probability due to coincidence has been estimated by the FBI, as noted above, but has not been published. Furthermore, as discussed in Chapter 3, this estimate is not 117   Like 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. 118   E.g., Vincent P. Guinn, NAA of Bullet-Lead Evidence Specimens in Criminal Cases, 72 J. Radioanal. Chem. 645 (1982); Vincent Guinn & M.A. Purcell, A Very Rapid Instrumental Neutron Activation Analysis Method for the Forensic Comparison of Bullet-Lead Specimens, 39 J. Radioanal. Chem. 85 (1977); A. Brandon & G. F. Piancone, Characterization of Firearms and Bullets by Instrumental Neutron Activation Analysis, 35 Int’l J. App. Radiat. Isot. 359 (1984). 119   See M.A. Haney & J.F. Gallagher, Differentiation of Bullets by Spark Source Mass Spectrometry, 20 J. Forensic Sci. 484 (1975); R.L. Brunelle, C.M. Hoffman & K.B. Snow, Comparison of Elemental Compositions of Pistol Bullets by Atomic Absorption: Preliminary Study, 53 J. A.O.A.C. 470 (1970). 120   See C.A. Peters, D.G. Havekost, & R.D. Koons, Multi-Element Analysis of Bullet Lead by Inductively Coupled Plasma-Atomic Emission Spectrometry, 15 Crime Laboratory Digest 33 (1988); E.R. Peele et al., Comparison of Bullets Using the Elemental Compositions of the Lead Component, Proc. Int’l Sym. On the Forensic Aspects of Trace Evidence, Quantico, Va., 1991; Charles A. Peters, The Basis for Compositional Bullet Lead Comparisons, 4 Forensic Sci. Communications No. 3 (July 2002). 121   See Raymond O. Keto, Analysis and Comparisons of Bullet Leads by Inductively-Coupled Plasma Mass Spectrometry, 44 J. Forensic Sci. 1020, 1026 (1999) (“This data suggests [sic] that when two element signatures match, it is unlikely that the bullets originated from different sources. The extent of each particular source (i.e., the number of identical boxes by each manufacturer) and the bullets available in a particular geographic area at a particular time are all unknown factors.”); Erik Randich et al., A Metallurgical Review of the Interpretation of Bullet Lead Compositional Analysis, 127 Forensic Sci. Int’l 174 (2002); William A. Tobin & Wayne Duerfeldt, How Probative Is Comparative Bullet Lead Analysis, 17 Crim. Justice 26 (Fall. 2002).

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence based upon an appropriately random sample of the bullet population. Laboratory error is another important factor in the false positive probability; the FBI has not estimated this factor and assumes it is essentially zero. In sum, the Daubert/ Kumho factor requiring a theory to have a known error rate is only partially satisfied. • The existence and maintenance of standards controlling the technique’s operation. The FBI has standards controlling the training of examiners, the laboratory protocol, and the statistical method for declaring a match. However, the laboratory protocol needs to be revised to reflect current practice.122 Moreover, the FBI does not have detailed standards governing the content of laboratory reports and the testimony that may be given by examiners. As a result, this Daubert/Kumho factor in significant part is not satisfied. • General acceptance in the relevant scientific or technical community. The analytical technique used (that is, previously NAA and now ICP-OES) has general acceptance of the scientific community for this sample type. However, to the committee’s knowledge the FBI is the only laboratory performing this type of lead analysis for forensic use, so any inquiry into “general acceptance” will not provide the broad consensus that this factor assumes. 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.123 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. But as the Court stated in Daubert, the test of reliability is “flexible,” and Daubert’s list of specific factors neither necessarily nor exclusively applies to all experts or in every case. Rather the law grants a district court the same broad latitude when it decides how to determine reliability as it enjoys in respect to its ultimate reliability determination.”124 However, the reliability and acceptance of the evidence would be strengthened if the FBI took the steps that the committee recommends. 122   Conversations with FBI examiners indicate that crime bullets are compared one-to-one with the suspect’s bullets and not with compositional groups of the suspect’s bullets as specified by the present protocol. 123   Attorneys have probably not challenged the evidence because the identifying link it provides to the same source is far from conclusive evidence that the defendant supplied the crime bullet. They often focus on the large number of bullets from a single melt rather than the technical intricacies of the matching process. 124   Kumho Tire, 526 U.S. at 141-142 (emphasis in original).

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence Defendant as Provider of Bullets As noted earlier, relevance in this context depends not only on an association between the crime scene bullet and the same melt as the suspect’s bullet but also on the further inference that this association suggests that the crime scene bullet came from the defendant. A conclusion that two bullets came from the same melt does not justify an expert in further testifying that this fact increases the odds that the crime bullet came from the defendant. The large number of bullets made from a single melt and the absence of information on the geographic distribution of such bullets125 precludes such testimony as a matter of expertise.126 Such an inference is a matter for the jury. An expert with distributional information might be able to provide such testimony to aid the jury. The available data do not permit any definitive statement concerning the date of manufacture or the identity of the manufacturer based on elemental composition alone. However, in some cases, boxes with lot numbers are recovered, which may provide some information on this issue.127 In other cases, physical (as opposed to chemical) characteristics of crime bullets are observed, which 125   See Jones v. State, 425 N.E.2d 128, 135 (Ind. 1981) (dissent) (“all retailers in a particular geographic area might consequently market bullets of similar composition”); State v. Noel, 697 A.2d 157, 163 (N.J. Super. App. Div. 1997) (“[T]he enhancement value to be placed on the same-batch conclusion must be basically a statistical probability exercise, that is, an assessment by the trier of fact of how much more likely it is that both sets of bullets were defendant’s because they not only matched in calibre and manufacture but also in composition. That assessment must necessarily depend on how many nine-millimeter bullets could have been produced from a single batch, what the likelihood is that those same bullets wound up for sale in the same geographical area, and what percentage of nine-millimeter bullets marketed in the Newark area came from Speers. Obviously, the strength of the link created by identical composition is a factor of how many bullets of identical composition were simultaneously available for sale in the Newark area, and, just as obviously, the statistical probability of defendant having possessed both sets of bullets declines as the number of identical bullets increases.”), rev’d on other grounds, 723 A.2d 602 (N.J. 1999). 126   The absence of distributional information also makes it inappropriate for an expert to testify that the probability that two bullets came from the same source if the defendant did not fire the crime bullet was described by the number of bullets made from the source divided by the total number of bullets of that type made in some period, such as 1 year. 127   State v. Freeman, 531 N.W.2d 190, 195 & n. 5 (Minn. 1995) (“This box of 50 cartridges contained the same loading code, 2TB90L, as the empty cartridge box found in the snowbank at the scene of Freeman’s arrest. This loading code indicated that the cartridges contained in both boxes were manufactured on February 9, 1982, during the second shift at Winchester’s plant located in East Alton, Illinois.”; “Also, both boxes were labelled with a Target price tag indicating a cost of $1.39.”). Lot numbers indicate the date of packaging, not the date the bullet was produced or the date the loaded cartridge was assembled.

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence may augment the probative value of the evidence.128 Also, “matches” of multiple crime scene bullets to multiple suspect’s bullets from different CIVLs may add to the probative value of the evidence in a particular case.129 Similarly, a case with a “closed set” of suspects presents a different situation.130 PRETRIAL DISCOVERY The need for pretrial disclosure of the nature and content of expert testimony is critical if the adversary system of trial is going to work. The American Bar Association (ABA) Standards note that the “need for full and fair disclosure is especially apparent with respect to scientific proof and the testimony of experts. This sort of evidence is practically impossible for the adversary to test or rebut at trial without an advance opportunity to examine it closely.”131 Never- 128   Physical characteristics include, for example, the caliber of the bullet, the number of lands and grooves as well as their direction of twist, and whether the bullet was jacketed or not. In some cases, empty cartridge cases are found at crime scenes, which would reveal the caliber and manufacturer as well as other information. E.g., State v. Ware, 338 N.W.2d 707, 712 (Iowa 1983) (“wadcutter bullet removed from Tappa’s body”); State v. King, 546 S.E.2d 575, 583-84 (N.C. 2001) (Firearms examiner, who also testified in case, “determined that a spent round submitted to him, as well as the live rounds recovered during the investigation, were .22-caliber long-rifle bullets. According to Agent Wilkes, the live rounds he examined were similar in physical characteristics to the lead bullet projectile removed from the victim’s wrist.”); State v. Noel, 697 A.2d 157, 160 (N.J. Super. App. Div. 1997) (“A bag containing eighteen bullets was found in [defendant’s] locker. Nine of the bullets were nine-millimeter bullets stamped with the manufacturer’s name, Speers. The police had also recovered spent bullets and bullet casings at the crime scene. The shell casings were also stamped with the same manufacturer’s name.”), rev’d on other grounds, 723 A.2d 602 (N.J. 1999); State v. Krummacher, 523 P.2d 1009, 1012 (Or. 1974) (“The bullet found in Dorothy’s body was identified as being a .38 caliber lubaloy copper-washed Smith and Wesson type bullet manufactured by the Western Company, which went out of business three years prior to the crimes in question.”). The combination of physical characteristics and analytic indistinguishability can be powerful evidence in a particular case. 129   Charles A. Peters, The Basis for Compositional Bullet Lead Comparisons, 4 Forensic Sci. Communications No. 3, at 5 (July 2002) (“Another factor that must be considered is a case where multiple shots of various calibers, manufacturers, and compositions are fired at a crime scene. 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.”). 130   A “closed set” case is one in which the universe of suspects is limited—for example, only one of two persons could have fired the crime bullet, so differentiation between ammunition from them is the principal concern. 131   Commentary, ABA Standards Relating to Discovery and Procedure Before Trial 66 (Approved Draft 1970). See also Paul C. Giannelli, Criminal Discovery, Scientific Evidence, and DNA, 44 Vanderbilt L. Rev. 791 (1991).

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence theless, pretrial discovery is often less extensive in criminal litigation than in civil cases.132 Federal Criminal Rule 16 governs discovery in federal trials. Four distinct provisions are relevant to expert testimony: scientific reports, summaries of experts’ expected testimony, other documents,133 and independent testing.134 • Reports. Rule 16(a)(1)(F) makes the “results or reports of physical or mental examinations, and of scientific tests or experiments” discoverable. Under this provision, reports are discoverable if they are either material to the preparation of the defense or are intended for use by the prosecution as evidence in its case-in-chief at trial.135 Unfortunately, the rule does not specify the content of a laboratory report. While the measurement data (means and standard deviations) on CABL evidence are discoverable, it is more logical and of greater use to include these data in the laboratory report. 132   Opponents 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. 2 C. Wright, Federal Practice and Procedure § 252, at 36-37 (2d ed. 1982). In the case of scientific evidence, however, these arguments against criminal discovery lose whatever force they might otherwise have. The first argument fails because “it is virtually impossible for evidence or information of this kind to be distorted or misused because of its advance disclosure.” Commentary, ABA Standards Relating to Discovery, supra, at 67. Moreover, it is extremely unlikely that an FBI expert will be subject to intimidation. See also 2 Wayne LaFave & Jerold H. Israel, Criminal Procedure § 19.3, at 490 (1984) (“Once the report is prepared, the scientific expert’s position is not readily influenced, and therefore disclosure presents little danger of prompting perjury or intimidation”). Finally, the self-incrimination clause presents little impediment to reciprocal prosecution discovery of scientific proof. See Williams v. Florida, 399 U.S. 78 (1970). In any event, it seems unlikely that defense experts will be retesting this type of evidence. 133   Rule 16(1)(a)(E) (formerly 16(1)(a)(C)) makes documents in the government’s possession discoverable—such as bench notes and graphs that may not be part of the final report. See United States v. Armstrong, 517 U.S. 456, 463 (1996) (“Rule 16(a)(1)(C) authorizes defendants to examine Government documents material to the preparation of their defense against the Government’s case-in-chief”); United States v. Zanfordianno, 833 F. Supp. 429, 432 (S.D.N.Y. 1993) (“A narrow view of Rule 16(a)(1)(C) is inappropriate; failure to provide reasonably available material that might be helpful to the defense and which does not pose any risks to witnesses or to ongoing investigation is contrary to requirements of due process and to the purposes of the Confrontation Clause. If an expert is testifying based in part on undisclosed sources of information, cross-examination vouchsafed by that Clause would be unduly restricted.”). 134   Independent testing has apparently not been a major issue in this context. 135   Virtually all jurisdictions provide for the disclosure of scientific reports in the possession of the prosecution. Scientific reports also are discoverable under the ABA Standards and the Uniform Rules. ABA Standards for Criminal Justice 11-2.1(a)(iv) (3d ed. 1996) (“Any reports or statements made by experts in connection with the case, including results of physical or mental examinations and of scientific tests, experiments, or comparisons”); Unif. R. Crim. P. 421(a) (Approved Draft 1974) (“expert reports”). See also National Advisory Commission on Criminal Justice Standards and Goals, Courts, Standard 4.9(3) (1973).

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence The conclusions in laboratory reports should be expanded to include the limitations of CABL evidence.136 In particular, a further explanatory comment should accompany the laboratory conclusions to portray the limitations of the evidence. 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 criminal justice system.137 Finally, measurement data (means and standard deviations) for all of the crime scene bullets and those deemed to match should be included. • Summaries. Rule 16(a)(1)(G) requires the government, on defense request, to disclose a written summary of the testimony of the experts that it intends to use during its case-in-chief. 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 cross-examination.”138 Although the ABA Standards recommend this type of discovery,139 most states do not have comparable provisions. • Conclusions. Like the NRC’s Committee on DNA Technology in Forensic Science, the present committee concludes that broad discovery is needed to the extent feasible: “The prosecutor has a strong responsibility to reveal fully to defense counsel and experts retained by the defendant all material that might be necessary in evaluating the evidence.”140 As one court put it, 136   Professor Anna Harrison, Mount Holyoke College, during a symposium on discovery, remarked: “Then the information you are receiving is not scientific information. For a report from a crime laboratory to be deemed competent, I think most scientists would require it to contain a minimum of three elements: (a) a description of the analytical techniques used in the test requested by the government or other party, (b) the quantitative or qualitative results with any appropriate qualifications concerning the degree of certainty surrounding them, and (c) an explanation of any necessary presumptions or inferences that were needed to reach the conclusions.” Symposium on Science and the Rules of Legal Procedure, 101 F.R.D. 599, 632 (1984) (emphasis added). 137   This recommendation will reduce the potentially misleading character of the evidence. See discussion of prosecution summary in State v. Noel, supra. 138   Fed. R. Crim. P. 16, advisory committee’s note, reprinted at 147 F.R.D. at 473. 139   ABA Standards for Criminal Justice 11-2.1(a)(iv) (3d ed. 1996) (“With respect to each expert whom the prosecution intends to call as a witness at trial, the prosecutor should also furnish to the defense a curriculum vitae and a written description of the substance of the proposed testimony of the expert, the expert’s opinion, and the underlying basis of that opinion.”). 140   National Research Council, DNA Technology in Forensic Science 146 (1992). See also id. at 105 (“Case records—such as notes, worksheets, autoradiographs, and population databanks—and other data or records that support examiners’ conclusions are prepared, retained by the laboratory, and made available for inspection on court order after review of the reasonableness of a request.”). The 1996 DNA report contains the following statement on discovery: “Certainly, there are no strictly scientific justifications for withholding information in the discovery process, and in Chapter

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence “there are no scientific grounds for withholding information in the discovery process.”141 A statement of the limitations of CABL evidence should be included in the laboratory report. Providing an express statement of the limitations of the technique in the laboratory report not only provides notice to the parties, it affords substantial protection for experts from overreaching by attorneys. Experts are sometimes pressured by the prosecutor to “push the envelope”—not a surprising occurrence in the adversary system.142 ABA Criminal Justice Standard 3-3.3(a) states: “A prosecutor who engages an expert for an opinion should respect the independence of the expert and should not seek to dictate the formation of the expert’s opinion on the subject. To the extent necessary, the prosecutor should explain to the expert his or her role in the trial as an impartial expert called to aid the fact finders….” The commentary to this standard states: “Statements made by physicians, psychiatrists, and other experts about their experiences as witnesses in criminal cases indicate the need for circumspection on the part of prosecutors who engage experts. Nothing should be done by the prosecutor to cast suspicion on the process of justice by suggesting that the expert color an opinion to favor the interests of the prosecutor.”143 FINDINGS AND RECOMMENDATIONS Finding: Variations among and within lead bullet manufacturers makes any modeling of the general manufacturing process unreliable and potentially misleading in CABL comparisons. 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.     3 we discussed the importance of full, written documentation of all aspects of DNA laboratory operations. Such documentation would facilitate technical review of laboratory work, both within the laboratory and by outside experts…. Our recommendation that all aspects of DNA testing be fully documented is most valuable when this documentation is discoverable in advance of trial.” National Research Council, The Evaluation of Forensic DNA Evidence 167-69 (1996). 141   State v. Tankersley, 956 P.2d 486, 495 (Ariz. 1998). 142   See Troedel v. Wainwright, 667 F. Supp. 1456, 1459 (S.D. Fla. 1986) (gunshot residue case) (“Next, as Mr. Riley candidly admitted in his deposition, he was ‘pushed’ further in his analysis at Troedel’s trial than at Hawkins’ trial. Furthermore, at the March 26th evidentiary hearing held before this Court, one of the prosecutors testified that, at Troedel’s trial, after Mr. Riley had rendered his opinion which was contained in his written report, the prosecutor pushed to ‘see if more could have been gotten out of this witness.’ When questioned why, in the Hawkins trial, he did not use Mr. Riley’s opinion that Troedel had fired the weapon, the prosecutor responded he did not know why.”), aff’d, 828 F.2d 670 (11th Cir. 1987). 143   Commentary, ABA Criminal Justice Standard 3-3.3(a) at 59.

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence Finding: The committee’s review of the literature and discussions with manufacturers indicates that the size of a CIVL ranges from 70 lbs in a billet to 200,000 lbs in a melt. That is equivalent to 12,000 to 35 million 40-grain, .22 caliber longrifle bullets from a CIVL compared with a total of 9 billion bullets produced each year. Finding: CABL is sufficiently reliable to support testimony that bullets from the same compositionally indistinguishable volume of lead (CIVL) are more likely to be analytically indistinguishable than bullets from different CIVLs. 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. Finding: Although it has been demonstrated that there are a large number of different compositionally indistinguishable volumes of lead (CIVLs), there is evidence that bullets from different CIVLs can sometimes coincidentally be analytically indistinguishable. Recommendation: The possible existence of coincidentally indistinguishable CIVLs should be acknowledged in the laboratory report and by the expert witness on direct examination. Finding: The available data do not support any statement that a crime bullet came from, or is likely to have come from, a particular box of ammunition, and references to “boxes” of ammunition in any form is seriously misleading under Federal Rule of Evidence 403.144 Testimony that the crime bullet came from the defendant’s box or from a box manufactured at the same time is also objectionable because it may be understood as implying a substantial probability that the bullet came from defendant’s box. Finding: Compositional analysis of bullet lead data alone do not permit any definitive statement concerning the date of bullet manufacture. 144   Testimony of Vincent Guinn, United States v. Jenkins, CR. No. 3:96-358, U.S. Dist. Ct., South Carolina, Columbia Div., Sept. 30, 1997, Transcript at 151 (Question: “Can you conclude if they match that the two bullets came from the same box of lead? [Answer:] “No, you can never do that. Every time they make a run from one particular melt, we are talking about a ton or more of lead involved. You can make an awful lot of bullets out of a ton of lead. So they get put in all these boxes and so on…. So, well, typically, for example, a one ton melt of lead will produce enough bullets, if it were just used itself, make enough bullets to fill something like 2,000 boxes of 50.”).

OCR for page 71
Forensic Analysis Weighing Bullet Lead Evidence Finding: Detailed patterns of distribution of ammunition are unknown, and as a result an expert should not testify as to the probability that a crime scene bullet came from the defendant.145 Geographic distribution data on bullets and ammunition are needed before such testimony can be given. Recommendation: The conclusions in laboratory reports should be expanded to include the limitations of compositional analysis of bullet lead evidence.146 In particular, a further explanatory comment should accompany the laboratory conclusions to portray the limitations of the evidence. 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 criminal justice system.147 Finally, measurement data (means and standard deviations) for all of the crime scene bullets and those deemed to match should be included. 145   See State v. Noel, 697 A.2d 157, 162 (N.J. Super. App. Div. 1997) (“Nor was any testimony offered as to marketing, that is, whether, as seems likely, bullets from the same billets would be shipped together by the manufacturer and hence that there would be a concentration of such bullets in a specific geographical region.”), rev’d on other grounds, State v. Noel, 723 A.2d 602 (N.J. 1999). The defense attorney in United States v. Jenkins, CR. No. 3:96-358, U.S. Dist. Ct., South Carolina, Columbia Div., Sept. 30, 1997, argued: “No company has still today provided us with any information from which we know whether all of this ammunition ended up in Columbia, South Carolina, or whether it was randomly distributed all over the country.” Transcript at 157. Testimony of Charles Peters, Commonwealth v. Wilcox, Kentucky, Feb. 28, 2002, Transcript, (Daubert hearing & trial testimony). Question: “And do we have any information as to the geographic distribution of these bullets?” Peters: … “Uh, I, I don’t know the information. I, uh, obviously, uh, uh, to answer that question would bring somebody in from PMC.” 146   Professor Anna Harrison, Mount Holyoke College, during a symposium on discovery, remarked: “Then the information you are receiving is not scientific information. For a report from a crime laboratory to be deemed competent, I think most scientists would require it to contain a minimum of three elements: (a) a description of the analytical techniques used in the test requested by the government or other party, (b) the quantitative or qualitative results with any appropriate qualifications concerning the degree of certainty surrounding them, and (c) an explanation of any necessary presumptions or inferences that were needed to reach the conclusions.” Symposium on Science and The Rules of Legal Procedure, 101 F.R.D. 599, 632 (1984) (emphasis added). 147   This recommendation will reduce the potentially misleading character of the evidence. See discussion of prosecution summary in State v. Noel, supra.