The door was the type that had to be locked when closed. If it was not locked, it did not stay closed.
Curt and Edda Knox are facing slander charges for publicly stating to the British media that Knox was deprived of physically and pyschologically abused for 54 hours. The only source for that information is Knox ... as neither her lawyers nor parents would make that up for no reason.
The evidence against all three culprits was sufficient for a jury or Judge (Guede's trial) to conclude that they are all guilty of murder. The evidence against Guede is not stronger than the evidence against the other two. However, if we eliminate all the forensic evidence, then the evidence against all three of them is equally weak. Guede admitted being in the bathroom at the time of the murder and the evidence proves that he was in the bathroom at some point.
Regarding the 54 hours:
"But Knox's lawyers say the Seattle native only confessed to being at home the night of the murder after nearly 54 hours of intense interrogation without a solicitor or interpreter. She later retracted her statement."
http://www.dailytelegraph.com.au/amanda-knoxs-lawyers-confident/story-fn6e1m7z-1225992691127
"Curt Knox said, "Amanda was abused physically and verbally. She told us she was hit in the back of the head by a police officer with an open hand, at least twice. The police told her, 'If you ask for a lawyer, things will get worse for you' and 'If you don't give us some explanation for what happened, you're going to go to jail for a very long time.'"
http://www.cbsnews.com/stories/2011/02/15/501364/main20031993.shtml