How can you assure that your roommate will pay for damages to an apartment you share.?

Okay, here's the story. My sister shares an apartment with her (ex)boyfriend. They are both on the lease. Recently he has become physically abusive to her and has punched holes in the walls, doors, cabinets of the apartment. She obviously does not live there anymore and has accepted the fact that she will have to may half rent until the lease is up. But now we are worried that her boyfriend will just leave the apartment in its severely damaged condition and she will get stuck with a huge bill. How can we make him pay for it?