To quote from a body language blog:
"No one hears a blood curdling scream, and doesn't know the source, but covers their ears. As humans, when we hear a threatening noise, albeit a scream, a loud bang or thud, we don't just decide to cover our ears without knowing what is going on. Our natural, biological response is to investigate the noise. It's a protective measure we all have within us, an instinct for survival, because that noise could ultimately be warning that we, too, are in danger.
We only cover our ears when we know what is going on, but don't want to listen to the wretched noise before us. This statement shows that Amanda had some awareness of what was going on when Kercher screamed. To me, that is bone-chilling. I don't think Knox lied about this bit of information. I suspect she was there and she did hear a scream, and perhaps she did cover her ears, but I believe she knew what was going on. It's too strange of a lie to come up with if she wasn't there or wasn't in some way involved. She just changed the details, and those details give her away."
The guy who admitted to killing her was a drug dealer. It is widely believed (nay, even accepted) that Knox was a drug taker. It is widely believed, from what she has said and her behaviour, that she required to be centre of attention and that she disliked the VICTIM Meridith, who had accused her of promiscuity and poor personal hygiene.
As a result, I firmly believe that, though she categorically did NOT kill the victim, she was by her own admission at the scene when it happened. Further, I believe that she set up the events by getting the drug dealer to come in and rape Meridith in revenge, in return for drugs. Did she know it would turn to murder? No. But she knew full well her "friend" was being raped and BY HER OWN ADMISSION IN COURT did not do anything to help or call the police.
Was Knox guilty of murder? No, but she was entirely complicit in the events, even if they turned out worse than she expected.