and all the samples had equal amounts of cerium, part of a compound used to ignite an oxyacetylene torch, a common item in machine shops. >> we examined all of them and could see the pattern that regardless of where they came from, they were basically the same kind of metal fragments, machining fragments. >> this proved that both arlene jensen and stephanie dittrick were killed by the same man. >> the science is starting to really catch up to the bad guys now. >> a serial killer was on the loose in the seattle area. he had to be stopped before he could kill again. >>> while investigating stephanie dittrick's murder, police interviewed the guests at her fourth of july party, the last time she was seen alive. they said stephanie spent most of her time talking to a man they did not know. >> while they didn't know his last name, they knew his name was gary. they knew that he bragged about being a drummer in a rock band. >> stephanie's family identified the man as her oldest and dearest friend, gary ackley. when interviewed by police, ackley recalled he was at the party but wasn't there speci