LE found a latent print outside of DM's room which was consistent with Vans shoe soles (as well as some Vans knock offs.) The print would be where the intruder walked according to DM. What we don't know yet is what size shoe print it was and what the latent print consisted of. We only know the latent print exists. Honestly, I'm unsure of how LE wasl be able to tell that the print is from that night versus all the nights of partying that went on in that house unless it is somehow a latent shoe print that contains blood. I guess we will hear about this when this case goes to court.
We know that it in all likelihood was left in blood, because they used a presumptive test for blood for round one, then for round two developed the print with a stain of Amido black to photograph it. Amido black reacts to the proteins.
Amido black 10B - Wikipedia
Finding a basic footprint in a house with plenty of residents and friends visiting all the time is to be expected. This was a house that was lived in. A random footprint, of which there would be many, would tell them nothing.
Finding a footprint IN BLOOD shows that it was left in the window of the bloodletting event. Now, you can't tell me they haven't tested that print for DNA, too. They would know whose blood it is, who were the contributor/s to it. I'm guessing the major contributors are Xana and/or Ethan, with maybe a little from the other girls, but mostly them, because of what we know about his movements through the home (thanks to D).
People who process crime scenes don't just randomly grab everything indiscriminately, they are trained for where to look and what to look for. They are looking for direction of movement, for places that would have been touched, for items that have been moved or removed, for patterns.
They knew the killer went to Xana's room, and left it. Xana and Ethan's bodies tell us that, and D's witness statement tells us that. So they would have been looking along that pathway, from Xana's room, past D's door, for evidence.
Also, as I think I've raised before, that point outside D's door is the one nexus of the home that you have to pass through when you want to go pretty much anywhere except the next room - from the top floor down, from the front to the back of the middle floor, from the kitchen to anywhere else... the only real movement that doesn't require going through that pinch point is from the bottom floor to the front half of the middle. And as far as we know, he didn't go downstairs to the bottom floor.
So, just theorising on movement, here - if he entered through the kitchen slider, went upstairs to Maddie's room, went back down to Xana's room, went back out through the kitchen, he passed though that pinch point three times. And two of those times was after a bloodletting event. I'd look there for a sharp print, too.
A reminder, I am not a CSI or forensics bod of any kind, just a giant nerd for it, so everything I have said above is my opinion only.
