Saturday April 25th is National DNA Day, marking the anniversary of the 1953 discovery of DNA’s double helix structure and the 2003 completion of the Human Genome Project. Today, the Death Penalty Information Center is pleased to present a new resource examining the controversial role of “junk science” in capital cases. When DNA testing became one of the most rigorously validated tools in forensic science, its development also prompted greater scrutiny of other forensic techniques. Many disciplines that were long accepted in U.S. courtrooms have now been found to lack adequate scientific foundation and have become known as “junk science.”
Of the 202 individuals listed on DPI’s Innocence List, 65 of these wrongful convictions and death sentences were based in part on junk science and flawed forensic evidence. Nearly 60% of these exonerees are people of color, and almost half are Black. The forensics used to convict these individuals includes arson investigation, ballistics and tool-mark analysis, bite mark comparison, microscopic hair analysis, and so called “Shaken Baby Syndrome” — techniques that most courts accepted for decades without question or rigorous scientific scrutiny.
Our new resources comprehensively examine each of these disciplines: the history of their use, how their reliability came to be questioned, and how they have affected capital cases. Among the cases examined is that of Cameron Todd Willingham, executed in Texas in 2004 based on arson evidence later shown to be premised on outdated and invalid methodology. Also covered is the FBI’s 2015 review of microscopic hair comparison testimony, which found that its expert witnesses gave erroneous testimony in 96% of cases reviewed — including nine cases in which prisoners had already been executed. On bite mark comparison, no court has broadly ruled the evidence inadmissible, yet bite mark evidence has contributed to more than two dozen wrongful convictions across the U.S., including capital cases. Regarding ballistics and tool mark evidence, a 2023 Maryland court recently ruled that a firearms examiner had overstepped scientific boundaries by testifying with “practical certainty” that shell casings matched a defendant’s firearm, a conclusion that the court found lacked sufficient scientific foundation.
DPI’s new resource also documents the evolution of the legal system’s approach to forensic evidence. The U.S. Supreme Court’s Daubert decision in 1993 established a new standard for the admissibility of scientific evidence, and a 2016 report from the President’s Council of Advisors on Science and Technology examined the limitations of several long-accepted forensic techniques. A 2023 National Institute of Justice study found that systematic errors across more than 30 forensic disciplines have contributed to wrongful convictions. Today’s courts increasingly recognize that scientific knowledge is not static, and what constitutes “junk science” may continue to change as understanding deepens, and analytical capabilities improve.
Learn more about these forensic disciplines at our Junk Science page.