. >> doctor terry melton is the founder of mitotyping technologies, a dna lab in pennsylvania. she conducted the test that led to joseph sledge's exoneration. >> if you think about the way microscopy is done on a hair, someone is deciding what color is that hair. microscopy is a very subjective science. and dna is exactly the opposite. you have atcgt and in the other sample you have atcgt. you line those 800 dna bases up next to each other, there's no gray area. >> when scientists figured out how to extract dna from hairs, in the late 1990s -- the fbi stopped relying on hair comparison evidence. but by that point, the bureau had introduced it at trials for decades, influencing thousands of convictions. in 2012, doctor melton's testing overturned two of those convictions, here in washington dc. both men had spent over twenty years in prison. >> i was arrested in august of 1978. >> and when did you go in, kirk? >> i went in, in '82. >> kirk odom was arrested for rape when he was 18 years old. santae tribble for murder, when he was 17. at odom's trial, an fbi agent testified that