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.

The tool: bite marks matching

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.”