to confirm that you were at a crime scene or that someone closely related to you — a sibling, parent or child, was at a crime scene. and that's the extent of what you can do with 20 markers. what we do at 0thram is we look at tens of thousands, to hundreds of thousands of markers, and with that information, we can detect more—dista nt relationships. every time you test for dna, you lose a bit of the sample in the process. in carla's case there was little of the killer's dna left. it was likely this was the last roll of the dice. we had to ask ourselves, "have we seen enough dna that is of this kind of quality and property, to where we feel confident that there's a good chance we'll have a positive outcome?" otherwise, we don't want to do it, cos when you test dna, you're consuming it, so you're destroying evidence. once they'd sequenced the killer's dna, they ran it through several genealogy websites. from there, they created a family tree of the killer. and then began to look