the witness, washburn.red all over the country, with the fbi's help, one by one, she tracked them down. >> we asked people. knocked on their door. literally, told them we were investigating a cold case and we'd like to eliminate you as a potential suspect. would you give us your dna? we had, in total, about 160 people that we got dna samples from. >> 160 samples. they all needed to be compared with the dna samples from the two crime scenes. easier said than done. isn't like the movies. this would take months. no idea if any of it would pay off. >> coming up -- so, first batch goes out there. none of these guys were a match. then, i send the next batch out and it's the same thing. >> weeks. months. a year of dead ends. then, came the phone call. >> i was like, no way. >> when "dateline" continues. getting ready for a special day? spice things up at adoreme.com. with bras and lingerie in sizes up to 4x. get on-trend bodysuits or lacy babydolls, just because. valentine's day special - sets start at just $19.95