Study cites errors, disagreements over bloodstain analysis

Crime scenes often contain bloodstains, and bloodstain analysts offer their interpretations as “scientific” evidence in criminal cases.

However, a new report published in the August 2021 edition of Forensic Science International says bloodstain pattern analysis (BPA) findings have an alarming error rate.

Popular media often portrays BPA in a false light

Many people remember the fictional character Dexter Morgan from the Showtime drama “Dexter,” who analyzed blood patterns at crime scenes (while also being a serial vigilante). Most TV shows and movies present BPA as incontrovertible evidence in criminal trials.

But researchers find the forensic technique is plagued by errors and disagreement among analysts. The study found BPA conclusions are often wrong, and analysts’ interpretations of crime scene blood evidence conflict in a disturbingly high number of cases.

“Erroneous and contradictory” results

In the most extensive study ever conducted in this discipline, researchers sent nearly 200 blood spatter examples and casework to 75 BPA experts for review. In cases with established causes of death, the study found:

• 11.2% of the experts’ conclusions were wrong
• 7.8% of the responses contradicted other analysts

A ProPublica investigation also raised concerns over BPA

In 2018, the nonprofit investigative Journalism organization ProPublica did a series of reports on BPA. It uncovered several red flags, including:

• Questionable casework
• Exonerations after wrongful convictions
• Investigators who testify in court with as little as 40 hours of training

For one of the stories, the reporter took a 40-hour BPA class.

No federal standards or oversight exists

A report by a presidential advisory council during the Obama administration recommended that BPA experts be required to disclose error rates during court testimony. However, the Justice Department rejected the proposal.

In 2017, under then-Attorney General Jeff Sessions, the department disbanded the National Commission on Forensic Science, which the Obama administration created to gauge the accuracy of forensic science offered as evidence in trials.

The new study links BPA to a growing list of forensic disciplines, such as shoe print, hair and bite mark analysis, that are widely accepted in courtrooms despite significant concerns over reliability and an alarming number of wrongful convictions.