Member
A little about DNA testing: I worked 26 years in a profession involving DNA testing. Mixed DNA takes time to sort out. There are advances since my technical work in this field so any WS member with updated info please correct me if my "old school" explanation needs an update. Crime scene DNA is collected, lots of it and it's labeled, (I'll leave out the highly scientific boring details). Through a series of incubation steps, with various temperature, pressure, and use of markers or tags, like fluorescence, and KNOWN DNA mixed with UNKNOWN DNA, results are interpreted after much time. KNOWN DNA is directly from a blood draw from the victims. UNKNOWN DNA is the scattered blood at the crime scene. Imagine the probably thousands of samples taken. Like attracts like, this is a natural scientific occurrence. The KNOWN DNA is split, (DNA is a double helix). KNOWN DNA is marked chemically with a tag visible usually something that illuminates and can be read microscopically or otherwise, (technical). So half of a KNOWN DNA strand is floating around in a mixture which includes an UNKNOWN sample from crime scene. A bonding will occur if there's a matching half in the mixture. The more strands that bond, the brighter the luminescence. Results without a "glow" are a negative match. There will come a point when crime scene samples won't match any victims. Then they'll look at the buccal smears collected, (or whatever method they've used to collect DNA samples from survivors. They'll test blood, skin cells, collected that doesn't match the victims. I apologize if this is confusing, it's complicated. Imagine a tray filled with same size circle shaped holes. Add a bowl of shapes; circles, squares, triangles. Rick the tray and the circles fill the holes, they match. Next tray is square holes, add the different shapes again and rock the tray. The square shapes fall and fit into the square holes. It's simplistic but not far off from DNA matching minus the positive and negative charges related to how the double helix connects.