![]() Are the statistical tests used to compare two samples appropriate? Can known variations in compositions introduced in manufacturing processes be used to model specimen groupings and provide improved comparison criteria? Is the method analytically sound? What are the relative merits of the methods currently available? Is the selection of elements used as comparison parameters appropriate? Can additional useful information be gained by measurement of isotopic compositions? In particular, the FBI asked the National Research Council to address the following three subjects and specific questions:Īnalytical method. The Federal Bureau of Investigation (FBI) asked the National Research Council to conduct an impartial scientific assessment of the soundness of the principles underlying CABL, the optimal manner for conducting an examination with CABL, and the scientifically valid conclusions that can be reached with CABL. If any of the fragments and suspect’s bullets are determined statistically to be analytically indistinguishable for each of the elemental concentration means, the examiner’s expert court testimony currently will indicate that the fragments and bullets probably came from the same “source.” The FBI examiner applies statistical tests to compare the elements in each crime-scene fragment with the elements in each of the suspect’s bullets. This process is used to determine the concentrations of seven selected elements-arsenic (As), antimony (Sb), tin (Sn), copper (Cu), bismuth (Bi), silver (Ag), and cadmium (Cd)-in the bullet lead alloy of both theĬrime-scene and the suspect’s bullets. The FBI examiner takes three samples from each bullet or bullet fragment and analyzes them by a process known as inductively coupled plasma-optical emission spectroscopy (ICP-OES). Crime scene investigators and autopsy pathologists collect bullet fragments (and sometimes a bullet in its entirety) from a crime scene or the body of a victim in order to compare them with unused cartridges in the possession of a suspect (suspect’s bullets) that investigators may have collected. One such approach is compositional analysis of bullet lead (CABL), which has been used by the law-enforcement community to provide circumstantial evidence for criminal investigation and prosecution since the 1960s. In such instances, a different approach must be explored to evaluate the possibility of a link between the crime scene bullet(s) 1 and the suspect. ![]() However, frequently, no gun is recovered, or a bullet fragment is too small or mangled to observe adequate striations. With bullets, this involves matching the striations on a bullet caused by its passage through the barrel of a gun with marks on test bullets fired through the barrel of a gun found in the possession of a suspect. Firearms examination focuses on characteristic marks left on fired bullets and expended cartridge cases by the weapon from which the cartridge is discharged. When a crime involves gunfire, examination of physical evidence derived from ammunition often yields key pieces of evidence used in the investigation of that crime.
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