Attempt to reason with him. Have him sign himself off of the lease and give him his stuff back. I would go as far as, i will move your stuff to where you want it, but you need to sign your name of off the lease. Technically, even thought the locks are changed he still has rights to be there. He can have the landlord let him in, if he refuses th police can tell the landlord he has to because it is this guys apartment too and you can not just ban him from it.

