Walter Kern

Walter Kern, AKA The Keystone Killer, was a serial killer who appeared in season one of Criminal Minds.

Background
Walter performed a series of murders in Philadelphia in the 80s. For a formerly unknown reason, the murders stopped. 20 years later, the killer again appears, but has changed his M.O. The original investigator of the case, Max Ryan (Gideon's mentor) refuses to take the case, and the BAU takes on the job.

Walter Kern had served in the military, and recently had done work as an home security specialist. He had recently gotten into an accident, where his spinal cord was severely damaged; leaving him with limited use of his right arm.

It is later revealed that Kern changed his M.O. due to his injuries in a car accident on the way to Carla Bromwell's house. His latest victims were all associated with Carla.

Modus Operandi
The unsub had changed his methodology, going from strangling with his bare hands and using a rope tied with an intricate knot; to hitting his victim over the head, suffocating them with a plastic bag, and binding them with flex cuffs.

Known Victims

 * 6 unknown women
 * Amy Jennings (last victim in the 1980s)
 * Carla Browning

Appearances

 * Season one
 * Unfinished Business