IDIOMS

thrill killer

(idiomatic) A murderer who is motivated by a strong personal desire to have a very exciting experience.

Example: 1954 Sept. 6, "SEQUELS: Another Life," Time:
  New York City's teen-aged thrill killer of 1945 was Lena Theresa Nienstedt, a whisky-drinking factory girl of 16. She carried a small hatchet in her handbag.
2011 March 29, Neil Genzlinger, "Farley Granger, Screen Star of the 1950s, Dies at 85," New York Times (retrieved 17 May 2013):
  [H]is best-known performances were two of his earliest: as a preppie thrill-killer in Hitchcock’s “Rope” in 1948, and as a tennis player wrongly suspected of murder in “Strangers on a Train” in 1951.