In the 1980s, a serial murderer targeted young men and left a trail of bodies across the Midwest. 

A duo known as the Serial Shooters stalked Phoenix, Arizona the same time the Baseline Killer did.

"Mark Of A Serial Killer," which returns to Oxygen on Sunday, October 17 at 7/6c, takes a deep dive into the most disturbing murder cases of all time.

In the 1980s, Larry Eyler, a vicious murderer who preyed on young men, became known as the Highway Killer.

In the 1990s, women were found dead in homes that had been set on fire across Chicago.

Between 1993 and 1998, a Chicago serial killer preyed upon women in the Englewood community.

Three women found dead in the Seattle area had ties to the nightclub scene — and so did their killer.

The so-called "I-95 Killer" pursued gay men and placed items like leaves, socks, and sex toys in their mouths after their brutal murders.

Steven Brian Pennell, also known as the "Route 40 Killer," picked women up off the highway before torturing and killing them.

Several serial killers wouldn’t leave the scene of the crime without taking something — be it a body part or a piece of jewelry — from the victim.