What about notification the dvm? As long as it is registered to you it represents a potential liability. I think I would at least talk to them. The guy is obviously taking you for a ride.

You may be able to at least cancel the current registration as it is in your name. I doubt he has insurance either.

You may need your copy of the bill of sale to attempt to get rid of those tickets as well. Requirements are somewhat different from region to region I imagine. At the same time you cannot have someone driving around in a vehicle registered to you. Unless you want to assume the responsibility for it.