>>session. >> welcome back to "dateline". i'm craig melvin. michelle martinko's unsold murder marked a loss of innocence for her friends and family. but not a loss of hope. cold case detectives were determined to catch the killer using a modern arsenal of tools. the same technology used to crack a legendary case in california, was about to reveal a tantalizing clue. back to dennis murphy with "and then there were three". >> the decades old investigation into michelle martinko's 1979 murder had emergency. detective doug larsson had a dna profile of the killer and the traditional list of suspects. one by one, he started asking for dna samples, looking for a match. >> doug started with the really obvious suspects. all the ex-boyfriends.