took police threatened to stop the investigation dead in its tracks. ♪ narrator: even though sierra bouzigard'speared to be sexually motivated, no dna was recovered from her rape kit. but thanks to sierra, the killer left his dna behind. she apparently fought off a sexual assault before being killed. the coroner was able to obtain a dna sample from under the fingernails of sierra. narrator: this meant the killer would likely be scratched up. even better for investigators, this dna profile matched other evidence at the scene. quaal: there was a profile obtained from a candy wrapper. that was a full profile, what we call a major-minor. the profile on the candy wrapper was a great quality profile. narrator: investigators knew that killers who resort to the kind of overkill seen in sierra's murder have usually killed before or have at least committed violent crimes, so they were confident they'd find a dna match to their killer in codis, the national dna database. well, i think we're going to solve it immediately. i think, "okay, if we put this in codis and we get a hit, then case solved." narrator