The Killer Inside Me by Jim Thompson - so dark and violent

Jim Thompson is an interesting writer. He grew up in East Texas in the 1900s when there wasn't much law or Church. His writing used to be hugely popular with Police Officers because Jim really did understand the criminal mind. Criminals are almost always stupid. They habitually overestimate their capabilities and underestimate the odds against them. For comparison read about The Dalton Gang who got annihilated by a bunch of farmers who happened to be tougher than the "desperados" who came to rob two banks at once.

Excellent