“For over thirty years, FBI experts testified about comparative bullet lead analysis (CBLA), a technique that was first used in the investigation into President Kennedy’s assassination. CBLA compares trace chemicals found in bullets at crime scenes with ammunition found in the possession of a suspect. (…) Although the FBI eventually ceased using CBLA, the Bureau’s conduct in first employing the technique and then defending it after it was challenged provides an insight into how forensic science sometimes works.”
Paul C. Giannelli
“Yet nearly a decade after the National Academy of Sciences report, little new work has been done to establish whether bloodstain-pattern analysis is actually a reliable forensic discipline. Few peer-reviewed studies exist, and research that might determine the accuracy of analysts’ findings is close to nonexistent. Meanwhile, experts with limited training continue to testify.”
Forensic science used in criminal trials can be surprisingly unscientific. Maybe a new television procedural could help change the public perception. Follow us on Twitter: @Intel_Today
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Should this type of forensic science remain in the courtroom?
The advent of DNA analysis in the late 1980s had not only transformed the future of criminal investigations; it also illuminated the past, holding old convictions, and the forensic work that helped win them, up to scrutiny. Rather than affirming the soundness of forensic science, DNA testing exposed its weaknesses.
Of the 250 DNA exonerations that occurred by 2010 throughout the United States, shoddy forensic work — which ranged from making basic lab errors to advancing claims unsupported by science — had contributed to half of them, according to a review by the Innocence Project. The sheer number of people who were imprisoned using faulty science called into question the premise of forensics itself. Just how reputable were these methods, and what exactly were expert witnesses’ opinions based on?
In 2009, the National Academy of Sciences sought to answer those questions with a groundbreaking, and damning, report. Its authors found that many forensic disciplines — including the analysis of blood spatter, hairs, bite marks, shoe and tire impressions and handwriting — were not as scientific as they often purported to be. Rather than being firmly grounded in hard data and rigorous, peer-reviewed research, many of these disciplines relied on the individual judgments of practitioners. The report included a sobering appraisal of bloodstain interpretation.
Analysts’ opinions were often “more subjective than scientific,” its authors warned, and open to “context bias.” They noted that “some experts extrapolate far beyond what can be supported.” Moreover, “the complex patterns that fluids make when exiting wounds are highly variable,” they observed, and “in many cases their interpretations are difficult or impossible.” In conclusion, the authors cautioned, “the uncertainties associated with bloodstain-pattern analysis are enormous.”
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