Synopsis

The serial killer known as BTK murdered people in and around Wichita, Kan., from 1974-91 and was finally caught in 2005, turning out to be a mild-mannered leader at a local church. The acronym described his modus operandi, which was to bind, torture and kill.

"Factor X," which takes its name from what the killer described in taunting letters to the police as his motive for murder, tells how a young, black counterterrorism expert from Washington teamed up with a Wichita police detective, who spent his career trying to chase down the killer.