Brandon L. Garrett, a law professor at the University of Virginia, has, for the first time, systematically examined the 200 cases in which DNA evidence has helped exonerate those wrongfully convicted. In each case, the evidence used to convict them was at least flawed and often false – yet juries, trial judges and appellate courts failed to notice. The study, “Judging Innocence,” is to be published in The Columbia Law Review in January, reports the New York Times. (Here is a link to the study: http://papers.ssrn.com/sol3/papers.cfm?abstract_id=999984)
The leading cause of the wrongful convictions was erroneous identification by eyewitnesses, which occurred 79 percent of the time. In a quarter of the cases, such testimony was the only direct evidence against the defendant. Faulty forensic evidence was next, present in 55 percent of the cases. In some of those cases, courts put undue weight on evidence with limited value, as when a defendant's blood type matched evidence from the crime scene. In others, prosecution experts exaggerated, made honest mistakes or committed outright fraud. Most of the forensic evidence involved problems with the analysis of blood or semen. Forty-two cases featured expert testimony about hair, an area that is, Professor Garrett wrote, “notoriously unreliable.” Informants testified against the defendants in 18 percent of the cases, and there were false confessions in 16 percent of the cases.