I agree with bringing all correspondence to the landlord and police. As well as tipping off the police to the party.

James mentioned that calling the police on roommate will mess him up for life... well... my view on that is, if he's involved in drugs, a party to child endangerment, etc.... he's brought it upon himself by breaking the law. Better to put a stop to it now, and help your case, than to ignore it and possibly suffer legal ramifications yourself. He's going to get caught sooner or later, I don't see anything wrong with helping that time be NOW.

Good luck, kiddo. This makes me SO GLAD I always lived alone in college. *shudder*