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Report: Bitemark Analysis Debunked as Pseudoscience

by Richard Resch

Unreliable bitemark identification evidence used in criminal cases has led to 31 exonerations, reports.

“The unsupported comparison of such bite marks left in human skin during rapes, murders and other violent attacks should be totally thrown out of forensic science,” says the magazine, citing a scholarly article by researcher and dentist C. Michael Bowers of the University of Southern California’s Ostrow School of Dentistry titled “Review of a forensic pseudoscience: Identification of criminals from bitemark patterns,” in the February 2019 edition of the Journal of Forensic and Legal Medicine. The analysis emphasizes that the “error rates of bitemark opinions are unknown: however, false positive identifications of defendants are now a fact.”

In addition, bitemarks change over time. For example, if the victim is deceased, the skin may slip as the body decays, causing the bite to move.

Consider Steven Mark Chaney. After serving 25 years of a life sentence for double murder, he was declared “actually innocent” by a Texas appeals court after bitemark evidence used against him was debunked. By late 2015, he was released.

His case sheds renewed light on this kind of evidence. M. Chris Fabricant, director of strategic litigation for the Innocence Project, told “The scientific community is unanimous in concluding that bite mark evidence has no place in our courtrooms and has all too often been used to destroy the lives of innocent people, convicting them for crimes they had nothing to do with.”

In Chaney’s case, the detectives ordered bite impressions of the suspect’s mouth after bitemarks were found on the left arm of John Sweek. Sweek and his wife Sally had stab wounds and slashed throats when detectives found them in their Dallas apartment around midnight June 20, 1987.

Chaney, police said, regularly bought cocaine from John Sweek and was in debt to him. Chaney, however, had nine alibi witnesses, reports.

Still, investigators zeroed in on the bite marks and ordered dental impressions from Chaney.

Dentist Jim Hales left no doubt he thought Chaney committed the murders when he told the jury “there was a 1-in-a-million chance that someone other than Steven Mark Chaney left the impression” on Sweek’s body.

However, the science used to convict Chaney has since been discredited, the dentist says, and the Dallas County district attorney’s office now calls bite-mark evidence “junk science.”

A 2009 National Academy of Sciences report, “Strengthening Forensic Science in the United States: A Path Forward” takes a dim view of bitemark analysis, and by 2016 “the Texas Forensic Science Commission recommended a moratorium on all similar bitemark evidence in the Lone Star State’s courtrooms,” reports.

“Hopefully this decision will be a turning point in purging unscientific and unreliable forensics, which has no place in any criminal trials, from our legal system,” Fabricant stated.

New protocols to “evaluate potential tooth impressions in skin” should help prevent wrongful convictions based on bitemark evidence, reports.

“Forensic Magazine has also reported other reversed convictions and prisoner releases related to bite-mark identification — like that of William Richards in California, who spent 25 years behind bars for his wife’s murder, and also Keith Allen Harward in Virginia, who had 33 years in prison for a rape and murder.”

Bitemark evidence needs to go the way of other now-debunked science, such as hypnosis-aided eyewitness statements, reports. “Human skin is malleable and changing, and thus impressions of teeth may always be inaccurate and should therefore not be admitted to courtrooms as identification criteria.”

In fact, what may look “like a bite can actually be an unrelated injury,” making bitemark analysis “subjective to the person evaluating the evidence,” reports. 




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