The hood and cape are from Darth Maul (but they're generic pieces), the face is Luke Skywalker (a nice solemn face), the pants are plain black, and the torso/arms/hands are from a bad guy from the Aquazone line.
The torso is not meant to be accurate to Garrett's costume. The most accurate torso I could find without modification (based on the Thief 2 scouting orb Garrett model) came from the Ice Planet line, but the colors didn't work as well for my movie (white sleeves and blue hands). I wanted the hands to be more visible, so I used a torso with red hands. Red hands are appropriate for a Thief anyway. :D
Garrett also wears an arrow quiver. It's the oldest one in my collection and conveniently bent a bit from use, allowing it to fit over the cape better than it would otherwise.

I know you didn't need that much detail, but the point is that Garrett isn't specifically from one Lego set.