Legal News

Appeal Court overturns sexual assault conviction because strength of DNA evidence overestimated

By Jason Siegel

The 9th U.S. Circuit Court of Appeals ruled that a man sentenced to life in prison must be freed or retried because the strength of the DNA evidence against him was overestimated by a prosecution expert, the Los Angeles Times reported.

Troy Brown was convicted of sexually assaulting a 9 year old girl in 1994, based largely on semen samples that a DNA expert testified had a 99.99967 chance of being Brown's. In 2004 another DNA expert rebutted that finding to a lower court judge and the 9th Circuit ruled 2-1 to upheld the decision, leaving prosecutors to free or retry Brown.

Legal experts told the Times that this was the first case in the country where a conviction was overturned due to what's known as 'prosecutor's fallacy', where "the prosecutor elicits testimony that confuses source probability with random match probability," the 9th Circuit judges explained.

"A prosecutor errs when he [or she] 'presents statistical evidence to suggest that the evidence indicates the likelihood of the defendant's guilt rather than the odds of the evidence having been found in a randomly selected sample," the court said. The court found that the prosecution's DNA expert underestimated the change that the DNA belonged to one of Brown's brothers, who had also been identified by the victim as the attacker.

Prosecutor's fallacy is possible in all DNA cases, the Times reported.

"Appeals court tosses rape conviction, criticizes scientist's DNA testimony," Reno Gazette-Journal

Full post as published by Legal Pad | LA on May 06, 2008 (boomark / email).