according to Brandon Garrett, a law professor at the University of Virginia and the author of Convicting the Innocent, eyewitness misidentifications have played a leading role in nearly 75 percent of 250 convictions overturned by DNA evidence between 1989 and 2010. In more than one-half of those exonerations, the eyewitnesses start off unsure, a “glaring sign” of potential trouble as Garrett puts it, yet appear to become increasingly certain over time. This often corresponds with police practices like suggestive photo arrays, lineups, and even well-intentioned comments like “Good job!” after a witness makes an identification, however tentative. All of this can cause “contamination” of memory, Garrett says so that “there is no way to know after the fact whether the eyewitness could have actually picked the person with any degree of confidence.”