I didn't like Mathis being made into a heavy, but that's today's cynicism for you. He wasn't suspected of anything in the book, but this is an adaptation. I wasn't surprised by the ending because I've read the book a number of times over the years so I don't feel anything was wrong. The film did give us a more punctuated ending than the book which I was quite happy with. If the film had indeed ended like the book, well, I'm not sure general audiences would have liked that.