They are secretly stalking America's streets and highways, hiding in plain sight and compelled by one simple motive: the thrill of taking another person's life. Since the 1970s, the United States has produced an estimated 1,400 serial killers--more than double the combined total of the rest of the world. What causes a seemingly normal human being to engage in serial acts of murder? This episode uncovers the psychological, biological and sociological make-up of these dangerous murderers. Why do they kill? How can they be identified and stopped before they strike? Former FBI profiler Clint Van Zandt, criminal psychologists Eric Hickey and Helen Morrison, journalists, scientists and law enforcement experts reveal the secret motives of serial killers like "BTK Killer" Dennis Rader and Jeffrey Dahmer--and explain why Ted Bundy, Donald Harvey "The Angel of Death" an the "Grim Sleeper" Lonnie Franklin Jr. were able to evade capture for years while they amassed a shocking number of victims.

According to government statistics, there are an estimated 5,000 cults currently operating in the United States. And each year there are approximately 200,000 Americans who serve as secret--and, for the most part, willing--members. But just what are these cults? And what makes some so dangerous? We'll uncover the psychological allure of cults, their charismatic leaders and insidious methods of controlling their members. How do ordinary people become trapped in these fringe groups, apparently unable to leave? Led by compelling self-proclaimed prophets, cults are clandestine, influential and all too often, destructive. Are their goals religious, political or simply financial? How and why does the government monitor or intervene in some cults--yet seemingly turn a blind eye to other's secret and perhaps sinister agendas? Jonestown survivor Tim Carter remembers the last day of Peoples Temple, and the horrific aftermath.