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Abstract
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orensic firearms identification involves linking evidence collected from crime scenes -- namely, fired cartridge casings and bullets -- to a particular firearm. Two assumptions underlie this identification process: First, firearms impart unique toolmarks on bullets and cartridge cases; and second, trained examiners can spot these marks and reliably determine that they were created by the same gun. Such testimony has played a central role in criminal trials for more than a century, connecting specific guns to specific crimes.1 But in recent times, the technique has faced increasing scientific and judicial scrutiny. This scrutiny is likely to increase as proposed amendments to Federal Rule of Evidence 702 -- which governs expert testimony in federal courts -- are set to take effect this December.
This essay summarizes a comprehensive review of more than 100 years of firearms comparison evidence case law. We first describe how judges' initial skepticism of the new methodology quickly transformed into near-universal acceptance, largely because confident experts displayed dazzling new technology, terminology, and techniques. But after decades of rote acceptance of the assumptions underlying firearms comparison evidence, judicial engagement and skepticism in the technique have surged. Of the judicial rulings discussing this kind of evidence that we reviewed for our comprehensive online database,2 more than half were penned after 2010. Several factors are associated with this uptick, including the release of several scathing reports by the National Academy of Sciences (NAS), the President's Council of Advisors on Science & Technology (PCAST), and the findings of new empirical studies that call into question the validity of firearm identification.
For the first time since 2000, the Federal Advisory Committee on Evidence Rules has proposed a set of amendments to Rule 702.3 The revisions specifically make clear that: (1) the proponent of an expert must show, by a preponderance standard, that various reliability requirements are met; and (2) an expert's opinions must be supported by a reliable application of trustworthy methods to data.4 These amendments stem from the committee's growing concerns over courts' failure to properly vet expert scientific evidence in criminal cases. The Advisory Committee notes emphasize that these revisions are "especially pertinent" to forensic evidence.5 Further, for forensic pattern-comparison methods, like firearms evidence, the committee noted that opinions "must be limited to those inferences that can reasonably be drawn from a reliable application of the principles and methods."6 The Rules Committee's proposed amendments to Rule 702 will take effect on December 1, 2023, unless Congress acts.7
The committee's amendments are likely to affect a wide range of types of expert evidence. By clarifying the burden on the party seeking to introduce an expert and highlighting the need to assure reliable use of methods to reach conclusions, the committee's concerns are particularly important in the context of forensic methods, like firearms evidence, that have grown out of the experience of practitioners but have never been carefully scientifically validated or subject to robust empirical testing. As we will describe, the rule change targets the two main concerns that judges have raised in that context -- (1) methodological reliability and (2) the overstatement of opinions in conclusions reached by experts -- in firearms evidence cases...
Language: en |