Sex conviction is overturned

A federal appeals court upheld a judge’s decision to overturn a sexual assault conviction on the grounds that a government scientist misrepresented the significance of DNA evidence.

In a 2-1 ruling, the 9th Circuit Court of Appeals said a Nevada sheriff’s DNA expert engaged in what is known as “the prosecutor’s fallacy� by equating the chance of a random DNA match in the general population to the likelihood that the DNA evidence came from the defendant.

The court said Troy Brown was convicted of sexually assaulting a 9-year-old girl in 1994 “most probably� because of “false but highly persuasive� testimony by the prosecution’s expert.

The analyst testified that DNA from the victim’s underpants matched Brown’s and that only 1 in 3 million people randomly selected from the population also would match. Pressed by the prosecutor, the analyst then testified there was a 99.99967% chance that Brown’s DNA was the same as the DNA on the underwear -- a probability of guilt that was not based on science, the court said.

-- Maura Dolan