It doesn't really matter if there was an arrest or not. The last registered owner (unless they can show different) is responsible for the disposition of the vehicle. If you were to sell a car, and the new "owner" doesn't transfer the title and just drives it around on "questionable" plates until it dies. When he leaves it on the side of the road the last owner will have the tow bill etc. charged against his credit until it gets cleared up.
In the case where the vehicle was involved in a hit'n'run, of course the current owner is the first investigated. Proof that he sold the car ended all probable problems of responsibility in either the accident or disposal of the vehicle.