Mark of a Serial Killer examines the disturbing behaviors of serial killers. Step into the minds of some of the worst serial killers to date as they taunt law enforcement. Some of these killers get a perverse gratification by habitually stealing mementos from murder scenes, including things like shoes, jewelry, keys, and even body parts. All of these stolen things are meant to taunt the investigators while the killers build up their notoriety. The killers often leave trademark clues behind as a way to mark something that was theirs, but the investigators often use these as clues to find them.