Firearm Forensics Continues to Face Challenges Due to Systemic Failures

Firearm Forensics Is Still Troubled by Systemic Failure

By Nicholas Scurich edited by Megha Satyanarayana & Dan Vergano

Each year, forensic firearm examiners play a pivotal role in thousands of criminal investigations, comparing spent bullets and cartridge cases to determine if they came from same gun. Their conclusions often carry immense weight in criminal trials, helping prosecutors secure convictions and send defendants to prison. Yet for decades, the validity of forensic firearm analysis has come under increasing scrutiny from research scientists.

Last October a debacle at the Rhode Island crime laboratory showed why. This is not just a story of incompetence—the case exposes deeper, systemic flaws in the discipline and how these flaws can jeopardize justice.

A fundamental principle of firearm examination involves analyzing “class characteristics,” the objective features shared by firearms of the same design, such as caliber or the lands and grooves in a gun barrel. If two cartridge cases don’t share the same class characteristics, they cannot possibly have come from the same firearm. This is a basic task that any competent examiner should perform without error.

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Yet in the Rhode Island case, three trained forensic examiners called a match between cartridge cases that had differences in class characteristics. This was not a subtle error; it was the forensic equivalent of declaring that two tires of entirely different sizes match the same vehicle. The fact that not one but three examiners overlooked such a fundamental discrepancy underscores a deeper problem: systemic issues embedded in the discipline’s methods, practices and culture.

One reason for these mistakes lies in visual confirmation bias—a natural tendency for humans to see what they expect to see. For example, when a scrunched image of 13 is quickly flashed to people, they interpret it as B when primed to think about letters, or as 13 when primed to think about numbers. Unconsciously using background information is an inherent feature of how people make sense of ambiguous stimuli.

Likewise, when examiners know the details about a case or have reason to suspect a particular weapon’s involvement—information commonly available to firearm examiners working in crime laboratories—they may unconsciously focus on similarities and ignore dissimilarities or conflicting evidence, such as mismatched class characteristics. This bias is especially dangerous in firearm forensics because there is no guidance for what marks to examine and focus on and no standards for how many similarities are needed to declare a match.

A Providence Journal image shows the marks on the breech face (the flat part at the back of a gun that holds the cartridge in place and stops it from moving backward when the gun is fired) that were noted by the outside expert who discovered the error in the Rhode Island case. Both the breech face marks and the rounded versus square corners apparent on the fired cartridge cases should have led the examiners to immediately conclude that the same gun did not fire these two cartridge cases. However, the examiners overlooked these differences, instead zooming in on the few markings that lined up to conclude that they were a match. They searched for confirmatory evidence so diligently that they failed to notice the difference in class characteristics. They lost the forest for the trees.

The problem was compounded by nonblind verification, a flawed practice where other examiners review evidence knowing the conclusions of the first. Instead of providing an independent check, nonblind verification reinforces errors, creating a feedback loop of confirmation rather than correction. In the Rhode Island case, once the first examiner declared a match, subsequent reviewers approached the evidence with the same expectation, making them overlook key class characteristic discrepancies. Indeed, the power of expectation is so strong that one examiner conducted two examinations of the same items and missed these differences both times.

Addressing these systemic vulnerabilities requires meaningful reform. First, firearm examiners must adopt practices that prioritize objectivity over expectation. For example, examiners should first document the class characteristics of an unknown item before they even begin comparing it to a known sample. This ensures that the most basic and essential criteria are met before subjective judgment comes into play. Only after confirming that the two items are comparable in their class characteristics should the examiner proceed to a comparison of finer details. This process, sometimes called linear sequential unmasking, helps ground conclusions in objective observations rather than expectations. While used in some European forensic labs, this process has yet to gain traction in the U.S.

Another critical step is ensuring that the process of verifying conclusions is genuinely independent. Too often, second examiners review evidence with the first examiner’s conclusions already in mind, creating a feedback loop where errors go unchallenged. Indeed, in 2023 a prominent firearm examiner testified that he had never seen a second examiner disagree with the first examiner in over 50 years of practice. Each examiner should analyze the evidence without any knowledge or inkling of previous findings. This approach breaks the cycle of rubber-stamped errors and ensures that conclusions are more rigorously vetted.

Finally, the discipline must move toward more scientifically grounded methods. Firearm identification relies entirely on subjective judgment, with no universal standards for interpreting marks on bullets or cartridge cases or declaring matches. Emerging statistical models and probability-based methods offer a promising path forward, providing quantitative measurements and thresholds to reduce subjectivity and improve consistency. While not yet ready for courtroom use, these innovations represent an essential step toward making forensic conclusions more scientifically grounded and reliable.

The failures in the Rhode Island case were not just the result of mistakes; they were the predictable outcome of a system that lacks safeguards against bias and subjectivity. By adopting objective, transparent and scientifically validated procedures, forensic firearm identification can start to move beyond its systemic failures, which imperil thousands of individuals each year. Justice demands nothing less.

This is an opinion and analysis article, and the views expressed by the author or authors are not necessarily those of Scientific American.