Mark of a Killer Season 4 is yet to be announced by Oxygen

Louisiana is terrorised by multiple serial killers in the 1990s; the Zachary Police Department find the key to solving their cases when they discover personal items missing from each local victim.

A serial killer taunts Wichita for decades with brazen letters taking credit for horrific kills; at the introduction of the computer era, the killer gets sloppy and leaves a digital clue.

The I-5 corridor in California is taken over by a brazen bandit who terrorises the highway with a blitz of assaults and murders; the only clue to the killer's identity is a specific athletic tape used to bind his victims.

Numerous women are found dead by the side of the road with a unique ligature that looks like a dog collar and leash; detectives are stumped until a 17-year-old girl manages an escape from a vicious kidnapper, leading police to a serial killer.

Police discover a string of murdered women in shallow graves in very remote areas of the Alaskan wilderness. After months of investigation, police zero in on a local family man living a double life.

A rash of young men go missing around Chicago during the 1970's. When bodies start washing up in the river a pattern emerges. A small piece of evidence leads police to the house of a model citizen where his furnace puts the suspect in the hot seat.

In the 1990s, New Yorkers are on edge as a killer leaves coded clues at crime scenes and declares his compulsion to choose victims based on their birth signs.

Brooklyn shop keepers are afraid of closing time as a killer shoots his victims while locking up their stores. Police release surveillance footage to the press and ask the public for help to find a Duffle bag wielding murderer before he strikes again.

In the summer of 1976, the NYPD are chasing a man shooting at couples in parked cars with a gigantic, .44 caliber handgun. He taunts the city with terrifying letters until police get a lead about a suspect who has shot a neighbor's dog. 

Twin Cities, MN, police are hunting for a killer caller who confesses to a string of murders in a chilling, high-pitched voice, begging for forgiveness. No one can identify him until one woman survives a brutal attack.

Texas authorities pursue a killer who rides the rails and leaves a literal trail of bread crumbs after eating at victims' tables. When more murders are linked, the FBI names a Most Wanted suspect and a national manhunt for The Railroad Killer ensues.

When the Hillside Stranglers are caught police realize they still have another serial killer running rampant in Los Angeles; he tortures and toys with his model victims while keeping pieces of their jewelry as he snaps their last photo ever.

A killer hijacks the highways of Sacramento as several women are found strangled with their clothing cut into precise but odd patterns; a survivor leads police to a sports car driving deviant posing as a good samaritan to poach potential victims.

Dallas police discover three women murdered with their eyes surgically removed; police believe they have a deranged doctor on the loose until two rookie cops find themselves on the trail of a man with a talent for taxidermy and a hatred for women.

In New Jersey four bodies are found dismembered, bagged, and thrown in roadside garbage cans. The "Last Call Killer" hunted his victims openly in piano bars but no one suspected he could be hiding in plain sight, working as a local nurse.

In 1990, a serial killer terrorizes the University of Florida's campus, killing 5 students in under 4 days. "The Gainesville Ripper" leaves behind a bizarre crime scene where all the victims have been stabbed but the females have been posed like dolls.