The Forensic of Firearms is still worried about the systemic failure

The Forensic of Firearms is still worried about the systemic failure

By Nicholas Scurich Edited by Megha Satyanarayana & Dan Vergano

Every year, Forensic Archinkers of firearms play a fundamental role in thousands of criminal investigations, comparing spent bullets and cartridge cases to determine if they come from the same weapon. Their conclusions often have an immense weight in criminal trials, helping prosecutors to ensure convictions and send the defendants to prison. However, for decades, the validity of the forensic analysis of firearms has been under increasing scrutiny of research scientists.

Last October a debacle in the Rhode Island Crimes Laboratory He showed why. This is not just an incompetence story: the case exposes deepest and more systemic defects in the discipline and how these defects can endanger justice.

A fundamental principle of the firearms exam implies analyzing “Class characteristics“The objective characteristics shared by firearms of the same design, such as caliber or the lands and grooves in a gun cannon. If two cartridge cases do not share the same class characteristics, they cannot come from the same firearm. This is a basic task that any competent examiner It must work without error.

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However, in the Rhode Island caseThree trained forensic examiners called a match between cartridge cases that had differences in class characteristics. This was not a subtle mistake; It was the forensic equivalent to declare that two completely different sizes tires coincide with the same vehicle. The fact that not one but three examiners will overlook such a fundamental discrepancy underlines a deeper problem: systemic problems integrated into the methods, practices and culture of the discipline.

A reason for these errors lies in visual confirmation bias: a natural tendency for humans to see what they expect to see. For example, When a wrinkled image of 13 It is quickly shown People interpret it as B When you prepare to think about letters, or like 13 When you prepare to think about numbers. The unconsciously use of background information is an inherent characteristic of how people give meaning to ambiguous stimuli.

Similarly, when examiners know the details about a case or have reasons to suspect the participation of a particular weapon, the information commonly available for firearms exams that work in crime laboratories, can unconsciously Focus on similarities and ignore differences or conflict evidence, such as the characteristics of the class not coincident. This bias is especially dangerous in firearms forensics because there is no guidance for what marks examining and focusing on and No standards For how many similarities are needed to declare a coincidence.

TO PROVIDENCE MAGAZINE image shows the brands in the Face of buttocks (The flat part on the back of a gun that keeps the cartridge in its place and prevents it from moving back when the gun is triggered) that the outer expert observed the error in the case of Rhode Island. Both the brands of the bedroom face and the rounded corners versus the apparent square corners in the cases of fired cartridge should have taken the examiners to immediately conclude that the same gun did not fire these two cases of cartridge. However, the examiners overlooked these differences, instead of approaching the few brands that were aligned to conclude that they were a match. They sought confirmatory evidence so diligently that they did not notice the difference in class characteristics. They lost the forest through the trees.

The problem worsened by not open verificationA defective practice where other examiners review evidence knowing the conclusions of the first. Instead of providing independent verification, non -cable verification reinforces errors, creating a feedback confirmation loop instead of correction. In the case of Rhode Island, once the first examiner declared a coincidence, the subsequent reviewers addressed the evidence with the same expectation, making them ignore the key characteristic discrepancies of the class. Indeed, The power of expectation It is so strong that an examiner performed two exams of the same elements and these differences were lost both times.

Addressing these systemic vulnerabilities requires significant reform. First, firearms examiners must adopt practices that prioritize objectivity on expectation. For example, examiners must first document the class characteristics of an unknown element before they even begin to compare it with a known sample. This ensures that the most basic and essential criteria are fulfilled before the subjective trial enters into play. Only after confirming that the two items are comparable in the characteristics of its class, the examiner must proceed to a thinner comparison. This process, sometimes called Linear sequential unknownHelp land conclusions in objective observations instead of expectations. While used in Some European forensic laboratoriesThis process has not yet won traction in the US.

Another critical step is to ensure that the process of verification of conclusions is really independent. Too often, the second examiners review the evidence with the conclusions of the first examiner that is already in mind, creating a feedback cycle where errors are not questioned. In fact, in 2023, an outstanding examiner of firearms testified that he I had never seen a second examiner in disagreement with the first examiner in more than 50 years of practice. Each examiner must analyze the evidence without any knowledge or idea of ​​previous findings. This approach breaks the cycle of rubber stamped errors and guarantees that the conclusions are more rigorously examined.

Finally, discipline must move towards more scientifically founded methods. The identification of firearms is based completely on a subjective judgment, without universal standards to interpret brands in bullets or cases of cartridge or declare coincidences. Emerging statistical models and probability -based methods Offer a promising path forward, providing quantitative measurements and thresholds to reduce subjectivity and improve consistency. While it is not yet ready for the use of the courtroom, these innovations represent an essential step to make forensic conclusions more scientifically founded and reliable.

Fallas in the case of Rhode Island were not just the result of errors; They were the predictable result of a system that lacks safeguards against bias and subjectivity. When adopting objective, transparent and scientifically validated validated procedures, the forensic identification of firearms can begin to go beyond their systemic failures, which imposes thousands of people every year. Justice demands nothing less.

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