Andrei Chikatilo(1936-1994)

Tortured, raped and killed at least 53 women and children (cannibalizing some of them) in Russia between 1978-90. It's believed that he actually raped and murdered at least twice that number, but due to police incompetence, negligence and the unwillingness of authorities to admit that such a killer could exist in a Communist state, he was able to continue committing his crimes for many years until he was finally caught--not by any investigative or scientific expertise but by a sharp-eyed policeman who noticed him acting "strangely" at a railroad station and detained him. It turned out that he had just that day committed three more murders.

What I did was not for sexual pleasure. Rather it brought me some peace of mind.