The most rigorous study ever done on a widely-used forensic technique – bloodstain pattern analysis (BPA) – reveals disturbing error rates and disagreements among certified analysts.
The study, published in the August edition of Forensic Science International, questions the accuracy and reliability of BPA, in which analysts interpret bloodstains at crime scenes.
The study sought responses from dozens of BPA analysts
Researchers sent nearly 200 photos of blood spatters from actual cases and control samples to 75 BPA analysts. Known causes were already established for each sample. The analysts offered their own findings, and researchers found two alarming results:
- 11.2% of the conclusions were wrong
- 7.8% contradicted other BPA specialists’ conclusions
BPA and other forensic evidence face greater scrutiny
Over the past decade, forensic methods over BPA, hair, shoe print and bite mark analysis have come under fire over subjective interpretations and a lack of established error rates. Still, courtrooms across the United States widely accept analysts’ findings as scientific evidence.
Concerns have surfaced before over reliability, and errors have led to wrongful convictions. In 2015, the U.S. Department of Justice admitted that two dozen FBI hair evidence analysts gave flawed testimony in hundreds of cases. Of those prosecutions, nearly three dozen defendants received the death sentence, and 14 were put to death or died in prison.
Justice officials reject calls to improve forensic standards
The Obama administration appointed the President’s Council of Advisors on Science and Technology to study forensic methods. The panel found a “dismaying frequency” of cases where forensic analysts’ conclusions failed to pass “an objective test of scientific validity.”
However, both the Obama and Trump administrations failed to act on recommendations to improve forensic standards, such as requiring expert witnesses to disclose error rates during testimony. The new study’s authors say using multiple analysts to reach a consensus instead of relying on one analyst’s conclusion may be helpful.
Also, researchers say standardizing the terminology and methodology used would likely reduce contradictory conclusions. But they add that the frequency and magnitude of mistakes should raise concerns for everyone, especially defendants in criminal cases.