My roommate scooter has been late with rent every single month I have lived with him. He also hasn't paid utilities for about 3 months. I have not seen him in about two weeks. So I changed the locks and told him I was going to keep everything in his room if he does not pay up. (about $1200 total). He is not on the lease. Today he finally showed up and wanted to take all of his possessions with out paying rent. I did not let him. What can I legally do or not do?

No, you can't just keep his stuff, that is stealing, you can file against him in court.

Give him back his stuff, if you want to sue him in small claim court do so.

Learn a lesson to get the right roommate