1. Assume the car is $20K and he own bank $5000.
2. You write a check to the bank for $5000 and seller for $15000. With the check to bank, you need a bill of sales and notice of title transfer.
3. Bank will issue you a title once the check is cleared.
4. You can register the car based on the bill of sale.
Make sure you have bank on the line while you issue the check. Assume seller does not want to cheat you, everything should be clear within 30 days.