We’ve all seen movies and TV crime dramas depicting bloodstain pattern analysis (BPA) as a scientific forensic technique, leaving little doubt as to “whodunnit.”
But a new study published in the August 2021 edition of Forensic Science International uncovers errors and disagreements among analysts over interpreting bloodstains at crime scenes.
The study shows many BPA conclusions are wrong
The study is the first-ever in-depth look at BPA, making it one of several forensic techniques to come under scrutiny, joining hair, bite mark and shoe print analysis. None of these so-called “scientific” methods have established error rates yet are widely accepted as evidence in courtrooms.
Researchers sent nearly 200 photos of blood spatter examples from actual cases and controlled samples to 75 BPA analysts for their review. On samples with established causes, 11.2% of the responses were wrong, and analysts contradicted each other in nearly 8% of the examples.
Previous concerns were voiced over forensic reliability
Until this study was released, a 2009 National Academy of Sciences review contained the most extensive research on BPA. It found bloodstain pattern analysis to be “more subjective than scientific” and urged extra care when using these analyses in court. In 2015, the U.S. Department of Justice was pressured to improve forensic standards after the FBI revealed:
- Two dozen examiners in one of its hair analysis labs gave flawed testimony in hundreds of court cases.
- Of those cases, 32 defendants received death sentences.
- Fourteen of these inmates either died in prison or were eventually executed.
In 2016, a presidential council urged the Justice Department to improve standards and require expert witnesses to disclose error rates when they testified. However, both the Obama and Trump administrations rejected those recommendations.
Independent reporting backs up these findings
The nonprofit investigative Journalism organization ProPublica did a series of reports on BPA in 2018. The key takeaways included:
- Exonerations of defendants wrongly convicted due to flawed analysis
- A disturbingly high amount of questionable casework and conclusions
- BPA analysts testifying as expert witnesses after only 40 hours of training
One of the ProPublica reporters even took the 40-hour class, which gave her similar credentials as the so-called experts.
Researchers once again offer recommendations over BPA
The study’s authors say while their research differed from actual casework, the error rate should raise concerns in the BPA community. They recommend standardizing terminology and methodology and having multiple analysts review casework instead of relying on one source.
