jailer (British also gaoler)
noun the jailer had discovered the loss of his prisoners:
prison officer, (prison) warden, (prison) guard, keeper, incarcerator, captor, sentry;
British (prison) warder, (prison) wardress;
informal screw;
Law detainer;
archaic turnkey.
jailer Oxford Dictionary of English 
EnglishOxford English Thesaurus
