How to Catch a Thief

Well, our house robber has struck again after we laxly left the door unlocked when we came home last night (this morning at 5 am, actually). He’s ventured farther into the apartment, opening two briefcase bags in the hallway and stealing 5,000 yen in coins from a basket tucked out of sight under a table in the hall.
So now I’m thinking of ways to catch this bastard in the act. Of course I will set up a motion detecting webcam to record any activitiy at the door. Perhaps I will also install a very loud buzzer to wake up not only us but every tenant in the building.
But what I really want to do is to invent a really novel way to incriminate him. I envision a Rube Goldberg contraption that sets off a chain of events when the door opens–a rope tied to the doorknob pulls upward as the door swings out, lifting a … what would you add to the machine and what would it do?