It is very difficult or impossible to prove Rudy Guede's actual motive for murdering Meredith Kercher, which he did by himself. (The crime scene analysis by Ron Hendry , a professional at that sort of thing, was of course not used at her trial, because it would have proven that Guede did it alone.)
I have written previously that he would have known that he would have to kill Kercher when he entered her room, because she would be able to identify him, and that up to the point where he entered her room, he had a choice of just strolling out of the apartment, perhaps even after flushing the toilet, without Kercher noticing or becoming alarmed. So, if he merely intended to steal some money, as most assume, he would have to be an utter moron to think that he could get away with it, unless he knew that he would be protected by friends in high places. They had apparenly been looking the other way during his crime spree leading up to the murder, so maybe he assumed that they would continue to do so in response to the murder. The police refused to testify during his trial about Guede's crime spree leading up to the murder, and about their respose.
I also find the claims about him being abandoned by his foster parents to be interesting. Why haven't they been implicated in any of what subsequently unfolded? Were the claims that they abandoned him, and that he was desperate for money, part of a cover story?
So, going over my recent previous posts and wondering if I've been playing too loosely with with motive, I still think that my scenario is as plausible as any, although it's possible that Mignini's response was opportunistic, and not pre-planned, and that his sympathetic attitude toward Guede was due to Guede's assistance in pinning the murder on Knox and Sollecito, and not an indication of a partnership that preceded the murder.