2. Kieran Kelly

For 30 years, Ireland's Kieran Kelly targets homeless people and transients, sometimes even pushing them into oncoming trains.

3. Ian Brady

After the deaths of murderers Ian Brady and Myra Hindley, news breaks that a briefcase left with Brady's lawyer may contain clues to his motives.

4. Sheila Labarre

Sheila Labarre invites men to her New Hampshire farm, where she abuses and murders them, leaving behind grieving families.

5. Douglas Perry

In 1990, a man named Douglas Perry kills three women. By the time authorities track Perry down, more than two decades later, Douglas has become Donna.

6. Todd Kohlhepp

Successful real estate agent Todd Kohlhepp hides a deeply disturbing life -- one in which he kidnaps, enslaves and kills.

7. Willy Inmon

A young man enters a police station, complaining of harassment from a neighboring town's police force. Later, that same man would confess to murder.

8. Elizabeth Wettlaufer

While working as a nurse for the elderly, Elizabeth Wettlaufer makes it her mission to kill the very people she's supposed to care for.

9. Theodore Johnson

After serving a sentence for killing his wife, Theodore Johnson is released from prison -- only to keep on killing.

10. Richard Dorrough

Before committing suicide, serial killer Richard Dorrough leaves a note in which he confesses to three murders. But did he actually kill more?