I think you should completely over-react to the situation. Put the car back in storage and get a mate to hide in the back with a months supply of food and some plastic bags to crap in. When the culprit finally gets in the back to sit when he's on his tea break your mate should violently kill him before bundling him in the boot, driving off and dumping the body in the foundations of the olympic village somewhere. Job jobbed.
If the car is locked up/alarmed or whatever and your the only one with the keys then it can only be you or a mate when you were giving them a lift
