On the murder knife issue:
1) Am I right to believe that kitchen knife from RS's apartment (i.e. one of the two alleged murder weapons) wasn't already in the girls' house on the night of the murder? In other words, is it generally agreed that the knife was brought from RS's flat to the girls' flat at some point on the evening of the 1st November? If so, I find it hard to reconcile why this would have happened, since the generally-agreed view of the crime is that it was not premeditated. I know that it's suggested either that AK was encouraged to carry the knife by RS "for her own protection", or that the knife was brought to the girls' flat to be used as a "threatener" in a sex game. But neither of those theories make much rational sense to me.
I do not think there is much that is agreed: and I do not think we can know whether the knife was brought there that night or at some other time. Knox was originally reported as saying the knife belonged to the cottage: but her flatmate(s) said they had never seen it there. The report might have been (probably was?) false, but either way it was quickly dropped and then it was said the knife was Sollecito's. I think most people assume it was taken to the cottage that night because the other women said they had never seen it: presumably they would have had it been there before? Not sure.
I also do not think it was carried for protection: I am not convinced it was a "sex game" either: but the possibility of a hazing along the lines that Knox was reported to have indulged in before seems possible to me. Per the web that is not very unusual in America, and although that is only one report (and I cannot find any verification for it) that is the fairy story which seems most likely to me, if I have to make up a story. On that scenario the reason that knife becomes plausible is precisely because it is big and scary: intended as a prop, and from a different house because Kercher would presumably recognise the cottage knives. But this is all just so stories: we do not know. It is terribly human to make a narrative but it does not add anything really
2) If this kitchen knife WAS used in the murder - why wouldn't AK/RS simply throw it away (perhaps even after careful cleaning)? Even if they thought they'd cleaned it so thoroughly that they'd destroyed any evidence, why would they take the risk? I am guessing that one reason they might have felt it necessary to retain the knife might be that some third party knew of Raffaele's ownership of it. Perhaps, for example, RS's mother had bought it for him as a housewarming present. Its post-murder absence might therefore have aroused suspicion. Does anyone know how many other people knew what types and numbers of kitchen knives Raffaele owned? I can only assume that SOMEONE knew he owned that kitchen knife - otherwise I can't understand why AK/RS wouldn't have cleaned it thoroughly and thrown it away. And after all, if nobody knew that this specific knife was connected to Raffaele, then even if it was subsequently found in a dumpster or a ravine, it's unlikely that it could be linked to RS/AK (unless, of course, they'd left evidence of themselves on the knife).
I have heard it said the knife came with his flat and was part of the furnishings there: but I do not know
