So what happened, who killed who?!

I think Catherine killed. She made everything so clever and intricate that there were no direct evidence against her. I believe she killed as her rich imagination and mental disorder made her do it. By the way she made great money with her books but money wasn't important to her and I think she enjoyed such life though wasn't happy.

SPOILER
Isn't it who killed "whom"? Anyway, I was confused myself. It couldn't have been the guy all along because when he finds the book and reads it and goes to save the psychiatrist lady he's obviously not faking it. Plus all those conversations betw. him and sharon stone would be stupid if he was the killer or they were both in on it. I hate movies where they put a whole bunch of crazy twists just to create suspense for the viewer when it doesn't make any sense with the plot. And who else thought it was stupid that the guy kept changing sides every 5 minutes. First he thinks it's the chick, then she tells him it's the cop so he believes her. Then the cop says it's the chick so he believes him, but (what a surprise) she tells him it's the cop again and so on. In the ending she tells him it's the cop so he shoots him but the cop with his dying breath tells him it was her so he's about to shoot her too but gets jumped by some cops before he gets a chance to. And in the ending the chick tells him it was him all along and he probably believed her then too. So idiotic...