Forensic Analysis Weighing Bullet Lead Evidence (2004) / Chapter Skim
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Executive Summary
Executive Summary
Pages 1-7
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, which has been used by the law-enforcement community to provide circumstantial evidence for criminal investigation and prosecution since the 1960s. Crime scene investigators and autopsy pathologists collect bullet fragments (and sometimes a bullet in its entirety)
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What are the appropriate statements that can be made to assist the requester in interpreting the results of compositional bullet lead comparison, for both indistinguishable and distinguishable compositions? Can significance statements be modified to include effects of such factors as the analytical technique, manufacturing process, comparison criteria, specimen history, and legal requirements?
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Recommendation: The FBI's documented analytical protocol should be applied to all samples and should be followed by all examiners for every case. STATISTICS FOR COMPARISON The FBI's documented statistical protocol for matching CABL evidences describes a statistical procedure known as "chaining." The chaining process 2 C.A.
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The full report examines the FBI's current statistical protocol and provides detailed recommendations about how it should be revised in order to provide a sound basis for determining whether crime-scene evidence and suspects' bullets are analytically indistinguishable. For example, within-bullet measurement standard deviations should be estimated using a pooled standard deviation over many bullets that have been analyzed with the same ICP-OES technique.
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SIGNIFICANCE OF THE MANUFACTURING PROCESS IN THE INTERPRETATION OF EVIDENCE The committee reviewed the lead bullet manufacturing process to determine whether known variations in lead compositions introduced in the manufacturing process can be used to improve CABL comparison data. In the United States, lead recycled primarily from car batteries is melted and refined at a secondary lead smelter to produce an intermediate lead ingot or billet.
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However for legal proceedings, the probative value of these findings and how that probative value is conveyed to a jury remains a critical issue. Despite the variations in manufacturing processes that make it difficult to determine whether bullets come from the same compositionally indistinguishable volume of lead (CIVL)
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The frequency with which coincidentally identical CIVLs occur is unknown. Chapter 4 includes findings and recommendations about appropriate statements that can be made in laboratory reports or by expert witnesses based on the committee's findings on analytical methods and statistical procedures and its knowledge of the bullet manufacturing process, including the following: · The available data do not support any statement that a crime bullet came from a particular box of ammunition.
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