The Collaborative International Dictionary of English v.0.48:

garroter \gar*rot"er\, n.
   One who seizes a person by the throat from behind, with a
   view to strangle and rob him.
   [1913 Webster]

WordNet (r) 3.0 (2006):

garroter
    n 1: someone who kills by strangling [syn: garroter,
         garrotter, strangler, throttler, choker]