T1, E1: This is the shocking and gruesome mystery of John Wayne Gacy, a popular Chicago businessman and part-time clown who was leading a double life in the 1970s. By day, Gacy was a community leader and helpful neighbor. But by night, he transformed into a monster who chose young male teens as his prey. How did this seemingly cheerful man become the most prolific serial killer of his day without anybody noticing and how was he ultimately caught?