Murder by Numbers

Police are puzzled by a pair of murders linked by a mysterious note, not realizing the killer has a target in mind.

In Billings, Mont., firefighters respond to a fire at a duplex and find two bound and gagged bodies; the victims' house mate is nowhere to be found, prompting police to question whether they're searching for the killer or another victim.

A woman is found murdered on the Appalachian Trail and her husband is missing, leaving authorities to wonder if he's the killer or another victim, then more bodies begin to appear.

Firefighters find the bullet-ridden bodies of Robert and Dorothy Pape while responding to a call about smoke billowing from a garage, in which they find a truck on fire; later, police realize the smoldering truck does not belong to the homeowners.

When a woman is found brutally murdered in her home, all signs point to a local troublemaker, then more bodies start piling up, making police realize they may be dealing with a serial killer, who is preying on the town's most vulnerable citizens.

In Amherst, N.Y., a missing college student's body is found hidden in the woods near a bike path, making the townspeople realize that the predator who has been stalking women for years has escalated from rapist to killer.

A monster hunts the streets of Baton Rouge, leaving three women raped, murdered and sadistically posed and everyone in town on edge. But when one brave woman survives a vicious attack, evidence leads police to the hunter and eventually justice.

A twisted murderer preys on young women in Bellevue, Wash., leaving their bodies sadistically posed. As police work to draw a crucial connection, an unconventional clue surfaces and leads them to an unlikely killer hiding in plain sight.

When a sheriff's wife answers the door of her Alexandria, Virginia home to a blaze of gunfire, theories buzz throughout the community. That is until more citizens are shot at their own front doors, leaving everyone wondering who could be next.

Within a month, four men in Orange County are brutally stabbed by a mysterious man. No one makes a connection to a gruesome double murder of a mother and son two months earlier - except the man sitting in prison for killing his own family.

Dallas has its dark side, but nothing compares the horror of a series of women found murdered with their eyeballs surgically removed. A pair beat cops use their street savvy to lead detectives to a sadistic killer and his bizarre motive.

A man is murdered by an intruder leaving his wife to witness a disturbing detail: the killer was wearing a clown mask. And when three more are killed by the same deranged clown, police realize they're dealing with a serial killer.

The busy streets of Atlanta, GA are shaken as horror of the "Necktie Killer" strikes the city with fear. Detectives from neighboring counties piece together correlative clues and distinctive apparel left behind at each crime scene.

A series of murders in California bear eerie similarities, but police have trouble connecting them—that is until unique ballistics, mysterious surveillance, and a bloody cell phone lead them to three criminals on a deadly revenge spree.