" Behavior reflects personality. The best indicator of future violence is past violence. To understand the "artist," you must study his "art." The crime must be evaluated in its totality. There is no substitute for experience, and if you want to understand the criminal mind, you must go directly to the source and learn to decipher what he tells you. And, above all: Why + How = Who. "

― John E. Douglas , Mindhunter: Inside the FBI's Elite Serial Crime Unit