I am not an Attorney, nor am I giving legal advise.

Experience with past like situations:

Send certified letter to the last known address. Keep a copy for your records. When the letter comes back, do not open it. Sell his stuff as "abandoned property".

I he comes back for it, hand him a Copy of the letter and a copy of the sealed certified envelope.

If he takes you to court, present the sealed certified letter to the court. The court will open the letter and inform the plaintiff that he was notified of the pending sale of property. He loses.

Frank