the witness, washburn.nd, though they were scattered 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, you know, 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. >> reporter: 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 are 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. tu. this isn't some dealership test drive around the block. it's better. this is seven days to put your carvana car to the test and see if it fits your life. load it