Legal Question in Criminal Law in Mississippi

It is not a criminal matter. If he co-signed he may try to assert some sort of a creditor's interest if you agreed to pay him back the down payment within a certain period of time and have failed to do so. The primary question will be "whose name is on the Title" as the Title will control ownership. If his name is "on the title" then he has an ownership interest. If both your name and his name are on the title then both of you have equal rights to the vehicle. If his name is not on the title then he most likely will be unable to assert a possessory interest in the vehicle unless he can show that you agreed to pay him his down-payment back and have failed to do so within the time period prescribed for repayment of the down-payment.

You will need to take a copy of the Title to a local attorney whose opinions you trust and let the Attorney advise you from here.