Good movie, BUT....

I actually enjoyed this movie - I really liked the sort of Agatha Christie who-done-it vibe, coupled with gore and horror.
Where it fell apart is towards the end, when we discover who the killer was all along. Spoilers:
How did Reddman escape when cops were crawling all over that place?
How did the true killer escape, and why didn't our heroine tell the police that she knew who it was straightaway?
How can you write a book about a crime, and unveil the murderer in said book, without going to the police first? Isn't that criminal? Aiding and abetting or something along those lines? And using that information to make money?
That's where it lost me. But other than that, good fun movie.