slayer,
killer a difficulty that is hard to deal with; "that exam was a real killer"
assassinator,
assassin,
bravo a murderer (especially one who kills a prominent political figure) who kills by a surprise attack and often is hired to do the deed; "his assassins were hunted down like animals"; "assassinators of kings and emperors"
butcher a person who slaughters or dresses meat for market
cutthroat someone who murders by cutting the victim's throat
liquidator One of the approximately 800,000 people who were in charge of clean-up after the April 26, 1986 Chernobyl disaster on the site of the event.