From The Collaborative International Dictionary of English v.0.48 [gcide]:
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]
From WordNet (r) 3.0 (2006) [wn]:
garroter
n 1: someone who kills by strangling [syn: garroter,
garrotter, strangler, throttler, choker]