executioner

noun

1. An official person who carries out the capital punishment of a criminal.

   “He would probably have died by the hand of the executioner, if indeed the executioner had not been anticipated by the populace.”

   “Underpinning that power was a reign of terror the like of which Chechens had not seen since the days of Stalin. Even the Russian contraktniki, or freelance fighters, were not as feared as Mr Kadyrov's private army of kidnappers, torturers and executioners were.”

2. (archaic)Executor.
3. A hit man, especially being in some organization.