Serial killers are real-life nightmares.

In the late 1940s, women answered personal ads thinking they would meet the man of their dreams. Instead, they met Raymond Fernandez and Martha Beck.

Aileen Wuornos’ experiences as a lesbian and abused sex worker have led many to consider her crimes as “justified" revenge against the men who wronged her.

"I was born with the devil in me."

Chillingly, he referred to killing young women as his "career."

He was Spain's first documented serial killer ... and the motivation behind his bloodlust defied all rational thought.

He was the sadistic killer behind one of the most chilling murder sprees in American history.

He claimed more than 24 victims ... but it was his method of murder that earned Haarmann his ghoulish moniker.

They called him "America's first serial killer of the modern era," but the case of the Boston Strangler is full of contradictions.

Lurking within this man of medicine was a ruthless killer who lured dozens of victims to their doom.

It takes two to make a thing go horribly wrong.

You thought you were scared of needles ... you had no idea.

May the odds be in your favor.

The crimes of these American murderers will make your skin crawl.

One woman's convalescent home came to be known as "the murder factory."

There have been several Night Stalkers over the years . . . but few were as chilling as the first.

John Christie was hanged for the murder of his wife ... but she was just one of his victims.

Four men were arrested for his crimes, but the real Monster is still at large.

By the time he was finally caught, this serial killer had claimed more than a dozen victims.

He was a serial killer, a serial liar ... or, most likely, both.

With these notorious killers, the disturbing details just keep coming ...