murderer, liquidator, manslayer

a criminal who commits homicide (who performs the unlawful premeditated killing of another human being)

• assassin, assassinator, bravo — a murderer (especially one who kills a prominent political figure) who kills by a treacherous surprise attack and often is hired to do the deed
• butcher — a brutal indiscriminate murderer
• cutthroat — someone who murders by cutting the victim's throat
• fratricide — a person who murders their brother or sister
• gunman, gunslinger, hired gun, gun, triggerman, hit man, torpedo, shooter — a professional killer who uses a gun
• hatchet man, iceman — a professional killer
• infanticide — a person who murders an infant
• murderess — a woman murderer
• parricide — someone who kills his or her parent
• ripper — a murderer who slashes the victims with a knife
• serial killer, serial murderer — someone who murders more than three victims one at a time in a relatively short interval
• Jack the Ripper — an unidentified English murderer in the 19th century

• criminal, felon, crook, outlaw, malefactor — someone who has committed (or been legally convicted of) a crime
• killer, slayer — someone who causes the death of a person or animal