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 he was a community leader and by night a predator of young men.

In Chicago, community leader and part-time clown John Wayne Gacy leads a double life, transforming into a monster who preys on male teenagers and becomes the most prolific serial killer of his day.

A look at the deal makers and hangers-on who attached themselves to Aileen Wuornos, who is known as America's first female serial killer.

The Zodiac Killer terrorizes Northern California in the late 1960s; he taunts the public with cryptic clues, threats of violence and ciphers that are supposed to lead to his identity, but mostly go nowhere.

The Zodiac Killer terrorizes Northern California in the late 1960s; he taunts the public with cryptic clues, threats of violence and ciphers that are supposed to lead to his identity, but mostly go nowhere.

In Northern California, a masked predator meticulously plans his sexual assaults by studying the habits and routines of his female prey; after 27 years on the loose, police close in on the man they believe to be the NorCal Rapist.

In Northern California, a masked predator meticulously plans his sexual assaults by studying the habits and routines of his female prey; after 27 years on the loose, police close in on the man they believe to be the NorCal Rapist.

A look at the deal makers and hangers-on who attached themselves to Aileen Wuornos, who is known as America's first female serial killer.

More than 900 Americans died in an isolated jungle in northern Guyana in November 1978; Jim Jones has gone down in history as a madman who drove his followers to suicide, but the truth is more complicated and tragic than that.

More than 900 Americans died in an isolated jungle in northern Guyana in November 1978; Jim Jones has gone down in history as a madman who drove his followers to suicide, but the truth is more complicated and tragic than that.

Charles Manson is a violent predator who has powers of persuasion that make it possible for him to convince his hippie followers to brutally murder innocent strangers

Charles Manson is a violent predator who has powers of persuasion that make it possible for him to convince his hippie followers to brutally murder innocent strangers