Motive is important because it's the reason behind the murder. If someone kills without motive, they are likely insane. I'm not saying she's innocent but the lack of motive sets off alarm bells for me. Knox lived in the same house in which the murder happened. Her DNA should be everywhere. it may be in places that are unexpected that would incriminate her but I think you still need to find some motive to close the deal. Someone must have some idea why an honor student would join with a drug dealer in a murder.