So SPOILERS ALERT...
... there were TWO murderers in the film, right? And also...
How exactly did the writer become a psychotic murderer later on, did that other killer have some kind of psychological influence over him or...?
Also, I love the film and all, but did you find that ending plausible, as in, would that detective really be fooled by SPOILER - a fake blood spraying knife and later be tricked by the killer like that?