“BTK Killer” Dennis Rader claims that a “demon” inside of him caused him to kill 10 people over a 17-year period in Wichita, Kansas. Nancy Grace explores that the 73-year-old serial killer says in the Oxygen documentary “Snapped: Notorious BTK Serial Killer.” Grace’s experts include medical examiner Dr. William Morrone, Southern California prosecutor Wendy Patrick, Los Angeles psycho analyst Dr. Bethany Marshall, Los Angeles lawyer Troy Slaten, Cold Case Research Institute director Sheryl McCollum, and Crime Stories reporter John Lemley.