You really haven't seen anything stating that the door needed to be locked with a key? Nothing at all, anywhere, not one mention of it? I'm surprised. Well, it's on PMF: try using the search engine and a few key words.
I have not seen that either. The door was faulty and inclined to open unless closed carefully. That may mean it had to be locked with a key from the inside or it may not. I do not really see how this helps us.
If you are correct and it needed to be opened with a key then what you are arguing is that Guede took the keys and opened the door with a key when he left the cottage. Was his blood on the door? On the door handle? We know that he was covered in blood and his bloody handprint was in Kercher's room.
Seem to me that there is a lot of uncertainty about this door. We do not know if Guede was admitted by a resident (Knox or Kercher). Or whether he arrived to find the door open, as Knox did the following morning (per her statement). We do not know if it was closed properly with the key after he arrived that night (assuming he was admitted by a resident). It could not have been if he arrived independently (unless we accept he came in through the window; and I find nothing in the evidence to support that contention, so I dismiss it: others differ, of course. )
As I understand it what you are proposing is that Guede acted alone: entered the cottage (by Meredith's invitation; by finding the door open; or through the window); assaulted and murdered Meredith for no reason whatsoever in a fight which left 47 injuries on her body; but did not allow her to fight well enough to get dna under her finger nails despite the fact that she was a student of martial arts; took the keys and the phones (but no other valuables:with the possible exception of the money, but there is no evidence that he took it); moved her handbag but did not open it, even though he had a pressing need for money with which to leave the country, on your thesis; opened the door with those keys leaving no trace so far as I am aware; ran away from his own house (as shown by where the phones, which were also free of any trace of blood, were found); went home and changed; and arrived at his friends house by 23:30 (I think that was the time: I am not prepared to spend the time checking it since none of this is new); and then went clubbing.
I see that this is plausible to you. It is not plausible to me.
But we are both in possession of the same facts, as is everyone else in this thread if they choose to be. You have brought nothing new.
This board is not about this case: it is about critical thinking. We present what we can find in terms of the evidence and reasonable interpretations of that evidence: and people form conclusions on the basis of that.
We have already heard what those who believe Knox (and Sollecito) to be innocent have to say on the "lone wolf" theory:and what those who do not believe it have to say.
What do you think is to be gained by going over the same stuff again?