Break his legs OR find a new roommate.
How to deal with aggressive roommate who steals, lies, and refuses to talk about it?
If the roommate is not on the lease change the locks, pack his / her stuff and put it all at the door.
Time to find a new roommate.
change the locks. JOKES. Don't do that. Find a new roommate if he/she 'refuses' to talk about it. That is not something you should have to put up with, hon.