Despite the criticisms, a series of new scientific studies show that forensic firearms analysis is a reliable scientific specialty that the criminal justice system should trust.
History of Firearms Analysis
Firearms analysis involves microscopic examination and comparison of fired ammunition samples (typically fired bullets and spent cartridge cases recovered from crime scenes), both with each other and with recovered firearms. Qualified firearm examiners can determine a specific firearm as one that may have fired a particular bullet or cartridge case. Investigators can then link firearms to shootings, and even connect one shooting incident to another. From New York to Los Angeles, hundreds of investigations into shooting incidents benefit every day from this analysis. Therefore, firearms identification evidence is essential for maintaining public safety and holding shooters accountable.
New Scientific Studies
Recent studies are based on a strong foundation from the initial study “Ames I,” showing remarkable accuracy in firearms identification. In fact, false positive error rates are below 1 percent, without technical review or verification to check errors. In other words, with a second set of trained eyes examining the evidence – as happens in actual work – the error rates in these studies would be very low.
Deliberate Challenges
In the “Ames II” study from 2022, 173 trained firearms examiners compared a total of 8,640 fired cartridge cases and bullets. The firearms and ammunition were carefully selected based on “their tendency to produce challenging and ambiguous test samples.” For example, the ammunition in the study had “cartridge cases made of steel and steel-jacketed bullets (where steel is harder than copper and less likely to mark).” With fewer microscopic markings, comparison becomes more difficult. Despite these challenging conditions, the overall false positive error rate was less than 1 percent.
Other Studies
Another study involving a larger number of participants led by Max Gaile from Arizona State University is notable for its results and chief authors. They were non-practicing – not forensic investigators at all – and had no legitimate interest in the outcome. In court, we refer to these types of witnesses as “independent” and “unbiased.” They asked 228 trained firearms examiners from across the United States to perform 1,811 microscopic comparisons of fired cartridge cases. These examiners worked in private labs, state county labs, and federal labs. The authors concluded that “the results revealed a very low false negative rate and a very low false positive rate.” Among 1,429 definitive decisions, there was one false negative and five false positive errors. No examiner made an error more than once. Again, the overall false positive error rate was less than 1 percent.
Amazing Accuracy
Study after study demonstrates the same reality: examiners are extremely accurate when identifying fired cartridge cases and bullets.
Uncertain Decisions
It is worth noting that measuring field integrity is its reliability in terms of inability to link fired ammunition to a firearm. Uncertain decisions are common in studies and in actual work. This is a feature, not a flaw, despite critics’ complaints in this regard. As the “Ames II” study explained: “Like any tool (the examiner is the tool), there are limits to their ability to interpret the quality/quantity of data/information presented.” It is clear that fired ammunition and fired cartridge cases do not always carry definitive markings supporting the inclusion or exclusion of a firearm.
Reliability in Courtrooms
This area applies reassuringly to firearms identification. When an examiner expresses the opinion that a fired cartridge case comes from a specific firearm, they are accurate over 99 percent of the time. Firearms identification evidence does not stand alone in a criminal case. It is just one brick in a wall of evidence that may include eyewitness testimonies, video surveillance, electronic location data, genetic evidence, among others. Moreover, unlike DNA analysis sometimes, ballistic evidence is never consumed and is therefore always available for re-examination.
Critics
And Justice
After the PCAST report, a few critics emerged. Some testified in pre-trial evidentiary hearings in an attempt to exclude or mitigate the opinions of firearms experts. These non-experts are not firearms investigators, nor are they practitioners in forensic science. They do not conduct any studies of their own. If these critics succeed where PCAST has failed – in convincing judges across the country to exclude firearms identification evidence – many victims of gun-related homicides may be denied justice.
Accredited Laboratories
Nearly 100 years after Goddard’s work, there are more than 200 accredited laboratories in the United States conducting firearms analysis. Analysts must follow approved standard operating procedures centered around quality assurance systems and undergo rigorous training that includes periodic proficiency testing.
Supporting Justice
As members of the National District Attorneys Association, we support the use of reliable forensic science to exonerate the innocent and prosecute the guilty. The prosecutors in the National District Attorneys Association, who are the “boots on the ground” in courtrooms across this country, know from experience that firearms identification evidence is scientific and withstands rigorous testing in the courtroom.
Conclusion
As John Adams, the American president and defense attorney, said: “Facts are stubborn things; and whatever may be our wishes, inclinations, or the dictates of our passions, they cannot alter the state of facts and evidence.” The facts, based on scientific studies, are that forensic firearms analysis is a reliable science that enhances the accuracy of the justice system.
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