What is incumbent upon me after repenting from stealing American film and song tapes, and is it permissible to invest the stolen money to pay for their value?

It is not obligatory to guarantee money that has been damaged from stolen unlawful possessions, nor to return it to the owner, lest he uses it for disobedience. Nor is it obligatory to give it in charity on his behalf, because unlawful things have no value in Islamic law. However, if the stolen item was permissible, then its substance or its value must be returned.