My roommate, or people my roommate's friends are stealing things.

I had an entire DVD collection taken from my apartment (they were in 2 giant DVD wallets), a Wii, and a towel rack go missing over the past couple of months. My other roommate had her digitial camera go missing. I asked the roommate in question if his friends went into my bathroom since they had been over the night it went missing. He said no. Later I noticed all my DVDs were gone, I asked if he had seen them, no again. And while I was gone over the break, he kicked and broke my door (not all the way, my other roommate stopped him). The only thing I have proof of is the door. Is there any sort of threat I can place on him to get his friends to return the stuff?

Updates
I've gone to the apartment office multiple times and keep getting the run around. My lease ends July 31st. While calling the cops over would be a good idea for prevention, I've kept my apartment pretty bare of valuables and left them at my mom's house. But I feel if I had the cops come over that he would never admit for fear of getting a record. Anyway I can scare him into giving them back? Before the door incident, my other roommate invited him and his friends to a party and his friends stole the keg and my roommate's friends were able to get it back by threatening to have their car towed and they said, "Well we don't have your keg, but we have one exactly like the one that was stolen...."