Well, issuing a small claim is pretty straightforward and not very expensive. I would get all the evidence from your locksmith re damage to the door, cost of repair (including what you haven't yet incurred) and issue proceedings. Include details in your claim of his actions when confronted by the damage (clearing out his room, etc., even though he wasn't due to leave). Judges aren't stupid.
If he submits a defence, then the matter will automatically be transferred to his home court (although you can apply for it to be transferred back on the grounds that the issue arose in your area, he was living in your area at the time, etc. - no guarantee they'll transfer it back, but it's worth a try). Chances are he won't defend, but will sh*t himself at not only receiving a visit from the police (nice one btw!) but also being sued. Might make him sober up too.