The autopsy (always to be crossed with other documents) tells me that there must be more than one perpetrator.
It's the most important thing.
The autopsy also reveals that Meredith was stabbed on the left with a knife which had a large blade.
The documents also show that Meredith was kneeling and facing the wall or the wardrobe, and the person who gave the fatal blow was between her and the bed. But someone else was holding her.
If you put together this with the fact that the metal clasp was forcedly deformed by Sollecito, the strap was cut with a small blade, it was cut before she received the first stabbing on the right but not removed, and a small knife poked her on her right, you have Sollecito's role.
In order to hold a large knife you need Amanda Knox. The person who stabbed her on the left side had not cut the bra (but the bra had been cut already), and the person who cut the bra is not Knox.
The person holding her wirst was Guede, he also committed a sexual violence usinge one hand, and another hand was pressed on her mouth.
There is also a number of other previous actions which require further hands (removing her clothes). In this system, Knox needs to be consistently placed on the murder scene playing an active role in this action. She is the one who was holding one big knife. The other two perpetrators are doing different things, they didn't give the left knife blow.
Just how did Raffael forcibly deform the clasp without leaving any DNA on the bra material?