As an innovator at the FBI in the late 1970s, John Douglas developed new investigative techniques for hunting serial killers, sex offenders, and other violent offenders. Advancing the use in investigations of the procedure known as criminal profiling, Douglas became widely recognized as its top authority. A mix of psychology, pattern recognition, and inductive/deductive reasoning, criminal profiling allows investigators to make educated guesses about suspects–sometimes accurately predicting their age, background, personality, and other identifying characteristics from the barest of clues. While leading the FBI’s Investigate Support Unit, Douglas used profiling...