Vengeance with heart
One of these: Holds 200 rounds
With a bunch of these: (four grams of extremely hot pepper powder (Capsaicin II) There used in riot control
Crank that Tippmann up to 350 fps, get 30 feet away, and wait. When the thief's show up, lay into them.
Not only will they be blind, barely able to breath, and burning; they will have half dollar sized bleeding welts that will also burn like hell as long as you keep firing.
I would have high doubts that the thief would fuck with anyone for a great length of time