their vehicles while off duty. so investigators tried to find some way to narrow it down. and latent evidence expert, ricky navarro, looked for clues on kim medlin's clothing. that's when he noticed a print on her sweatshirt. >> at that point in time, i could not determine whether i was looking at a footwear impression or some other type of object that left that impression on the sweatshirt. >> using alternate light sources and high-speed cameras, navarro concluded he was looking at the heel of a shoe. >> it was a type of shoe that was not flat from toe all the way back to the heel. it had a distinct heel in it which, like some of your hard-soled shoes would have, not like your athletic shoes would have. >> and there was a distinct "v," or chevron pattern, across the print.