BULLET FORENSICS EVIDENCE MAY BE FULL OF HOLES
July 20, 2004
For several years, statisticians, metallurgists, and others outside the FBI have questioned the courtroom use of bullet chemical analyses. Now, a National Academies' report combined with past studies detailing the forensic tool's shortcomings, could call into question many past convictions in which results of the chemical analysis of bullets was introduced as evidence.
The report found:
- Bullets with the same chemical composition are estimated to come from the same pot of molten lead; however, data shows that chemical composition among bullets vary within a single pot, and that bullets from two different pots could be chemically alike.
- Manufacturers receive slabs of lead from different smelter pots, which is then cut into bullets, but FBI research reveals that one box of bullets can contain as many as 14 various chemical compositions due to the variance in slabs.
- In areas where there are few bullet retailers, the chance that an innocent buyer purchases a bullet with similar chemistry to that of a suspect's bullet is great; in Juneau, Alaska -- where there are only three bullet retailers -- the chance ranges from 87 to 100 percent for each brand of bullet.
Legal experts have questioned the accuracy and reliability of other forensic techniques, such as handwriting analysis, tool-mark analysis, and even fingerprint analysis. Moreover, David Faigman of the University of California's Hastings School of Law recommends that all forms of forensic sciences, including psychological evaluations (repressed memories and battered women's syndrome) be critically evaluated in light of the National Academies' report.
Source: Alexandra Goho, "Forensics on Trial: Chemical Matching of Bullets Comes Under Fire," Science News 165, no. 13, March 27, 2004; National Research Council of the National Academies, "Forensic Analysis: Weighing Bullet Lead Evidence," National Academies Press, 2004; and Alicia Carriquiry, et al., "Statistical Treatment of Class Evidence: Trace Element Concentrations in Bullet Lead," Iowa State University, October 10, 2002.
For National Academies report http://www.nap.edu/books/0309090792/html/
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