Murder By Numbers

A pair of murders linked by a mysterious note puzzles police as they scramble to stop a budding serial killer. What they don't realize is the murderer has a target in mind, and nothing, not even a growing body count, will stand in his way.

When Billings, Montana, firefighters respond to a duplex consumed in flames, two bound and gagged bodies are found inside. With their housemate nowhere to be found, police aren't sure if they're searching for the killer or another victim.

When a woman is found murdered on the Appalachian Trail, and her husband is missing, authorities are left wondering if he's the killer or another victim. But when more bodies begin to disappear, it's clear a deadly predator is stalking in the woods.

When firefighters are called to a blazing truck, what they find in the house pales in comparison -- the bullet-ridden bodies of Robert and Dorothy Pape. And the heat turns up when police realize the extinguished truck belongs to someone else.

When a woman is found brutally murdered in her home, all signs point to a local troublemaker. But when more bodies start piling up, police realize they may have a serial killer at large -- preying on the town's most vulnerable citizens.

When the body of a missing college student is found hidden in the woods along the Amherst, New York, bike path, locals realize that the predator who's been stalking women in the area for years has escalated from rapist to killer.