" By studying as many crimes as we could, and through talking to the experts—the perpetrators themselves—we have learned to interpret those clues in much the same way a doctor evaluates various symptoms to diagnose a particular disease or condition. And just as a doctor can begin forming a diagnosis after recognizing several aspects of a disease presentation he or she has seen before, we can make various conclusions when we see patterns start to emerge. "

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