The body was behind a locked door,true. But Knox and Sollecito were cleaning up in the bathroom with bleach which they had bought specifically that morning before they even considered calling Police.
Cleaning a bathroom is not unusual. There was a leak and he volunteered to help her deal with it. If they were going to clean up evidence they would have not left any evidence to be found because they would have no way to distinguish their bloody prints from Guede's and certianly could not remove their own DNA and Semen from her body yet leave his.
There is nothing at all to establish any collusion among them. No testimony from any party, no evidence that any of them ever phoned, emailed or wrote to eachother ever and nothing to demonstrate Sollecito even knew him. The only evidence of Knox meeting him is when ALL the girls who lived with Knox met him when they were in the flat below and he visited.
The only evidence was against Guede, the prosecutor was embarrassed that he was wrong about Knox and made up the notion she invited Gued over from wholecloth. There is nothing at all to suggest such let alone to establish it beyond a reasonable doubt.
The court decision which exonerated her was very thorough and well supported. That shoudl ahve been the end, there was no error in law committed by that court so nothing to reverse on appeal. The Court of Cassation reversed by finding factual error though the Court of Cassation has no authority to make such findings. It is not a Supreme Court which has the authority to decide the facts for itself it is stuck with the facts determined below. That alone makes the retrial where she was convicted again highly unusual and improper.
The actual findings of the court that reconvicted her are not supported by any evidence. There was nothign at all to establish period let alone beyond a reasonable doubt that Knox decided to kill Kercher for calling her dirty and decided to invite Guede to come help kill and rape her. Guede says Kercher invited him and they had consensual sex before Knox arrived. There was thus no testimony to suggest she let him in or invited him. Nor was there any other evidence to suggest such- no evidence they ever communicated by phone, email etc.
It is blatantly obvious that Guede broke in and raped and killed her on his own.