My father died and the person I sold the bike to stole his license plate. What can I do?

So my father passed away 2 years ago and we just recently sold his bike to a former teacher of mine. When he got the bike I forgot to get Dad’s license plate off of it. I told the buyer I needed it back and he told me he would bring it in a couple of days. 1½ weeks has gone by. I saw him in town and asked him again and he said he would bring it in a couple of days again. The plate does not have to be returned to the state of Tennessee but I don’t want someone having a plate that was my father’s. I sold the bike to him for far less than it was worth and waited 11/2months for him to have the funds to buy it. I have been overly kind to the buyer. What should I do? Do I call the police and tell them the situation? He told me the second time I asked about it that it was in the garage of his friend’s.