IDIOMS

thrill kill

(attributive, usually hyphenated) Of, pertaining to, or being such an act of murder.

Example: 1988 March 9, Sheridan R. Hansen, "Police arrest 2 Utah Count teenagers for questioning in Las Vegas shooting," Deseret News, p. B3 (retrieved 17 May 2013):
  "It was a thrill kill. Robbery was an afterthought. This is one of the most senseless murders we've had down there in years."
2012 April 12, "Supreme Court Hears Appeal of Colin Koehler's Life Sentence," WABI TV (retrieved 17 May 2013):
  "[T]his essentially was a killing for no reason, a thrill kill. . . ," said Attorney Donald Macomber.
2007 Sept. 23, David Bowman, "Torchlit Crit," New York Times (retrieved 17 May 2013):
  We all know that plenty of kids took to Route 66 after reading “On the Road,” but few juveniles committed thrill-kill murders after paging through “Crime and Punishment.”