A Leading Cause for Wrongful Convictions: Experts Overstating Forensic Results


More than 150 men and women in American prisons were exonerated in 2018, according to a recent report by a registry that tracks wrongful convictions. Combined, these individuals spent more than 1,600 years in prison, a record for the database, which has data back to 1989.

The leading culprit in convicting innocent people was official misconduct, according to the report by the National Registry of Exonerations. Nearly one third of these cases involved a police corruption scheme in Chicago through which a police officer framed individuals on drug charges.

Another prominent factor in wrongful convictions across the country was misleading forensic evidence. A close look at these cases reveals how experts in fields like hair analysis, bite marks and DNA analysis have used exaggerated statistical claims to bolster unscientific assertions.

Once experts meet the qualifications to take the stand in a courtroom, there are few limits on the words that come out of their mouths.

In court, a lab analyst testified that the hair on the butcher paper had a 1 in 2,700 chance of matching someone other than the victim, and the hair on the tablecloth had a 1 in 48 chance of belonging to someone other than Mr. Payne. He then multiplied these figures together to get a “1 in 129,600” chance of anything other than a random occurrence.

In 2017, lawyers who were reinvestigating the case reached out to the analyst. He acknowledged that the statistical evidence was invalid. He said he should have indicated “that the hair sample found on the defendant could have come from the victim, and the hair sample found on the tablecloth used to cover the victim could have come from the defendant.”

A new medical report also suggested that the charges were a product of a misunderstanding. The little girl wasn’t suffering from abuse, it concluded: She had a strep infection.

Ms. O’Brien said bite mark analysis was even more bogus than hair comparisons. Often you can’t even tell if a wound is a bite mark, she said. “It doesn’t even get past the barest suggestion of scientific reality.”

This pseudoscience cost Steven Chaney decades of his life. In 1987, Mr. Chaney was charged with murdering a couple who sold him drugs.

At trial, a medical consultant testified that he’d compared a wax model of Mr. Chaney’s mouth to a mark on the male victim’s arm. Mr. Chaney’s upper and lower arches “matched” the bite, he said, adding that “only one in a million” people could have made that impression.

In 2018, an appeals judge concluded that “scientific knowledge underlying the field of bite mark comparisons has evolved” since Chaney’s trial “in a way that contradicts the scientific evidence relied on by the State at trial.”



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