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.

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.

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.

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.

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.

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.

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 1990, Florida police search for the so-called Interstate Killer, but the case goes cold and there is no end in sight.

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 Chicago, businessman and part-time clown John Wayne Gacy leads a double life; by day, he is a community leader and helpful neighbor, but, by night, he's a monster who preys on male teenagers as one of the most prolific serial killer of his day.

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.

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.

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.

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.

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.

In Chicago, businessman and part-time clown John Wayne Gacy leads a double life; by day, he is a community leader and helpful neighbor, but, by night, he's a monster who preys on male teenagers as one of the most prolific serial killer of his day.

Host Donnie Wahlberg chronicles the twisted lives of diabolical criminals, such as Charles Manson, Aileen Wuornos, John Wayne Gacy, the Rev. Jim Jones, and others.

Host Donnie Wahlberg chronicles the twisted lives of diabolical criminals, such as Charles Manson, Aileen Wuornos, John Wayne Gacy, the Rev. Jim Jones, and others.

Uncovering the dark and twisted motives that led to gruesome killings in the pursuit of a deeper understanding of the relationships behind the horrific killings and of the psychology of the people who committed them.