The Collaborative International Dictionary of English v.0.48:

Captor \Cap"tor\, n. [L., a cather (of animals), fr. caper to
   take.]
   One who captures any person or thing, as a prisoner or a
   prize.
   [1913 Webster]

WordNet (r) 3.0 (2006):

captor
    n 1: a person who captures and holds people or animals [syn:
         captor, capturer] [ant: liberator]