The scientific reliability of FBI hair analysis has been questioned as DNA testing has exonerated persons convicted where the only physical evidence was hair analysis. In addition, in a high percentage of cases, the FBI has learned that its expert witnesses overstated the reliability of hair analysis in testimony in court cases. In 2013 the Department of Justice began a review of thousands of cases from 1982 through 1999 referred to the FBI for hair analysis. By 2015 it found that these included 32 death penalty convictions, of which 14 people had died in prison or been executed, and narrowed its review to cases that went to court. It has focused on cases in which hair analysis played a part in convictions, in order to follow up with defendants.