(n.) One who massacres.

Cain alarmist apache assassinator bloodletter bloodshedder bomber bravo burker butcher button man cannibal cutthroat desperado eradicator executioner exterminator garroter gorilla gun gunman gunsel hatchet man head-hunter hit man homicidal maniac homicide killer man-eater man-killer manslayer massacrer matador murderer pesticide poison poisoner scaremonger slaughterer slayer strangler terrorist thug torpedo trigger man