His(or someone elses) finger prints were wiped clean off the drug kit he had with him when he died.
His suicide note wasn't all in his handwriting, but the part that wasn't in his writing wasn't courtneys either.
He had mentioned that he feared for his life before he died.
I wouldn't put it passed that bitch courtney. I'll see if I can find the website that has all the stuff on it.
Edit: Here's a nice link
http://www.anomalies-unlimited.com/Kurt_Cobain.html
I have a theory why Courtney DIDN'T kill him. He made her, Ever hear a good Hole song recorded after he died? She needed him too much. I dunno, it sounds like good arguement for people who think she didn't have something to do with it.