Forensic science of firearms is still plagued by systematic obstacles

Forensic science of firearms is still plagued by systematic obstacles

By Nicholas Skarich Edited by Megha Satyanarayana & Dan Bergano

Every year, forensic firearms examiners play a pivotal role Thousands Of the criminal investigation, compare used bullets and cartridge cases to determine whether they came from the same gun. Their conclusions often weigh hugely in criminal trials, helping prosecutors secure convictions and send defendants to prison. For decades, however, the validity of forensic firearm analysis has been exposed to an increasing number of scrutiny from research scientists.

The big failure last October Rhode Island Crime Research Institute He provided the reason. This is more than just a story of incompetence. This case reveals deeper and systematic flaws in discipline and how these flaws put justice at stake.

The basic principles of firearm inspection include the analysis of “.Class characteristics“The purpose of firearms of the same design share, such as land and ditches in calibres and gun barrels. If two cartridge cases do not share the same class of characteristics, they cannot come from the same firearm. This is A competent examiner is the basic task Must run without error.

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still Rhode Island Casethree trained forensic examiners called coincidence between cartridge cases, with differences in class characteristics. This was not a subtle error. It was forensic to declare that two tires of completely different sizes match the same vehicle. The fact that we do not overlook such a fundamental contradiction is the fact that such fundamental contradictions highlight a deeper problem. It is a systematic issue embedded in methods of discipline, practices and culture.

One reason for these mistakes lies in visual confirmation bias. This is a natural tendency to see what humans expect. for example, For a crouched image 13 It will flash immediately For people, they interpret it as b When prepared to think about letters or As 13 When you’re prepared to think about numbers. Unconsciously using background information is an inherent feature of how people understand ambiguous stimuli.

Similarly, if the examiner knows the details of the case, or if there is reason to suspect the involvement of a particular weapon (information commonly available to firearm examiners working at a crime lab), they are unconscious. In Focus on similarities It also ignores conflicting evidence, such as incongruent class characteristics. This bias is particularly dangerous in forensic science for firearms. There is no standard For the similarities needed to declare a match.

a Providence Journal image Displays the mark of Bleach’s face (The flat part behind the gun that holds the cartridge in place and stops it moving backwards when it is fired) External experts who discovered the error in a case in Rhode Island pointed out . Both the breech’s face marks and round and square angles, apparent in the fired cartridge cases, should have come to quickly conclude that the same gun did not fire these two cartridge cases. However, the examiners overlooked these differences and instead zoomed in on some markings lined up to conclude that it was a match. They searched very enthusiastically for specific evidence and did not notice differences in class characteristics. They lost the forest due to the trees.

The problem has gotten worse by this Open-label verificationflawed practice of reviewing evidence that other examiners know the initial conclusion. Instead of providing independent checks, open-label validation enhances errors and creates a feedback loop of confirmation rather than corrections. In the case of Rhode Island, when the first examiner declares a match, subsequent reviewers approach the evidence with the same expectations and overlook the contradictions of key class characteristics. surely, The power of expectation It was so strong that one examiner conducted two exams on the same item, missing both of these differences.

Meaningful reform is needed to address these systematic vulnerabilities. First, firearm examiners should adopt practices that prioritize objectivity over expectations. For example, examiners should first document the class characteristics of unknown items before comparing them with known samples. This ensures that the most basic and important criteria are met before subjective judgments unfold. If the examiner proceeds to a more detailed comparison, only after confirming that the two items are comparable to the characteristics of the class. This process is sometimes called Linear Sequential Unmaskingfundamentally supports the conclusion of objective observation rather than expectations. While using Some European forensic labsthis process has not yet gained traction in the US.

Another important step is to ensure that the process of verifying conclusions is truly independent. Often, the second examiner reviews the evidence already with the first examiner’s conclusion in mind, creating a feedback loop where errors are not challenged. Certainly, he was a prominent firearms examiner in 2023. I never saw the second examiner disagree. He was the first judge after more than 50 years of practice. Each examiner should analyze the evidence without knowledge of previous findings or inkling. This approach breaks the rubber error cycle and ensures that conclusions are examined more closely.

Finally, discipline must move towards more scientifically grounded ways. Firearm identification has no universal criteria for interpreting bullet or cartridge cases, or marks of matching declarations. New statistical models and probability-based methods It provides quantitative measurements and thresholds to provide promising paths to advance, providing less subjectivity and greater consistency. Although not yet ready for use in court, these innovations represent important steps to make forensic conclusions more scientifically grounded and reliable.

The failures in the case of Rhode Island were not the only consequences of mistakes. They were predictable outcomes of systems that lacked protection against bias and subjectivity. By adopting objectives, transparency and scientifically validated procedures, forensic firearm identification may begin to move beyond the systemic obstacles that put thousands of individuals at risk each year. there is. Justice demands less.

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