We have the ILE techs on tape passing the fragment of bra clasp from person to person and then putting it back down on the floor. That's a half-dozen or so different sets of gloves touching the clasp. Where had all those gloves been, is the question, not whether the defense can prove theoretical contamination?
We already know AK saw the broken window, but didn't call police. I think she was intimidated by the prospect of trying to report a break-in in a language she didn't speak. So she turned to RS and FR, both fluent in Italian.
Obviously, her right foot stepped in something her left foot missed. I don't know what. I believe there has been a vehement argument as to whether it was blood.
I don't know why you find this a "smoking gun." AK has admitted to showering and wandering around the apartment on the morning after the murder.
I agree this needs to be explained, but I don't see how any of it is incriminating to AK or RS.
I think if those three pieces of evidence can be disproved then there is nothing left of substance to say they are guilty. That's actually a pretty small amount of information to disprove, compared to where it started (where in fact, there was nearly a dozen pieces of evidence that indicated they were guilty, which were then proven completely untrue... such as a clean up).
1) As with Otto, I cannot claim to be an expert on DNA. But the report reads that they collected cigarette butts, which had a high concentration of Sollecito's DNA, the butt of which was adjacent to another cigarette, and none of the DNA got jumbled in this scenario. They also said that shed cells, which is what gets floated around in dust, cannot show a fresh sample like it did on the bra clasp. The amount of DNA, and the quality, indicated that this DNA came from non-shed skin cells that arrived on the metal. This as indicated by some socks found in the same place that had no migratory DNA on it. Therefore, if it occurred from contamination, it would have to be something like (my best guess) turning a door handle sollecito touched, then handling the clasps in such a manner that it would transfer to the clasps. In addition, this would have to have occurred only in this instance and in no other. That's my best understanding of it, and I will fully admit I'm not sure I know what I'm talking about. I'm hoping someone who really knows what they are talking about will come on and explain to me why I should dismiss it.
2) The luminol evidence did reveal evidence of cleaning, though it was clearly prior to the murder (regular cleaning). When did this cleaning occur? If just prior to all this, we wouldn't expect to see anything that had occurred until the cleaning took place. We also know (from Meredith's own words) that Amanda didn't keep the bathroom clean. If you read the report, it does say that luminol testing is done 6 weeks after specifically so things like bleach won't flouresce. But if it WAS blood, then we would expect Meredith's DNA to show up in every footprint. I mean it is a whole footprint left from blood, instead of a tiny bit on the tip of a knife. I would assume that she had stepped in bloody water residue, but I'm not sure that's enough to flouresce (she stepped into residue underneath the bathmat, that was still damp?). I actually know a CSI guy and he told me that would never happen, but I'm not sure I explained it properly.
3) I think the break-in can be explained as a true break-in. But if the evidence indicates Rudy left, and someone else stayed and cleaned themselves up, and locked the doors, then that's a big problem. If we can say it's very suspicious that there is no DNA of Amanda or Raffaelle in the murder room (though there is one piece still in play actually), then it would follow that it is very suspicious that there is no DNA evidence of Rudy in the bathroom. NOW, contrariwise, my neighbor did say that water is the best way to get rid of DNA, so maybe bathrooms are in general a poor place to retrieve DNA. And the only reason Amanda and Meredith can be found everywhere is because it is their bathroom.