You must send the former tenant a letter, certified, informing him that he has up to X date to remove the belongings left behind in the property or you will have to take action as permitted by the your state law. Add to the content of the letter that if items are not removed by the X date, you will have to put the items in storage and the filing of a claim in small claims court will ensue so you can recover the costs of removing and storing the items. He will get the message pretty quickly...