Come on. 'Crazy' people do not act like this. (spoilers)
Sociopathic? Sure.
But if he was truly crazy enough to believe his fantasy (that last scene), he would not have been functioning well enough to pull any of this stuff off.
If it was "all in his head" and he never left the mental institution, that was a complete cop out by the filmmakers.
Someone can be homicidal and lack conscience without being "insane." You can have delusional thinking (which he didn't) and not have hallucinations (if he was to the point of hallucinating, there is no way he'd be able to maintain his job, his relationship, his lies and his friendships). Sane people do not have vivid hallucinations. This is a pet peeve of mine - when "insanity" functions almost like the Hand of God. I suppose others may enjoy it, but for me, it's predictable and frustrating. I really wish the cops had ****MAJOR SPOILER*** come to ambush him the same as they did, and he'd burned the house down, but without the final showdown/Jessica Alba nonsense.
I liked this movie throughout. I thought there was some extremely lazy investigating on the part of the police, but overall, the movie was believable and the characters realistically flawed. Until the last 15 minutes - then it lost about 4 stars. 5 out of 10 from me.
They're coming to get you, Barbara!