The Killer Inside Me, by Jim Thompson
Recently made into a movie for the second time (which was released just last summer), Jim Thompson's 1952 literary crime classic The Killer Inside Me is a harrowing journey into the mind of its protagonist Lou Ford. Seemingly at first nursing a grudge against the millionaire whom he seemingly believes murdered his brother, Lou, a deputy sheriff in a small but corrupt town in Texas, sets off a chain of events with one killing after another. Possibly due to mistreatment as a child by his father's mistress (which he uses as an explanation for some of the killings) , Lou suffers from "the sickness", which got him in trouble as a youth and now manifests itself in his adult life. At first Lou's "sickness" is focused towards the millionaire but quickly spreads to anyone -friends, strangers, even loved ones- who threatens his freedom.
As the bodies start piling up and wary authorities try to poke holes in his various alibis, Lou, a true sociopath, tries to justify to himself and us the reasons for his murder spree. During the course of the novel we start to worry along (and take sides) with Lou as to whether he'll actually get caught or not. Subsequently, both Lou and the readers are broadsided by the shockingly powerful surprise climax. Violent, nasty and thoroughly engrossing from start to finish, The Killer Inside Me holds your attention with nail-biting suspense that never lets up.
(P.S. Thompson was a darn good writer. Check out the other books by him that we carry, like The Grifters, plus two we don't: The Getaway and Pop.1280.)