I just went through this in Virginia
I bought a 66 Mustang that had changed hands 4 times and never retitled. I had to go to the DMV and file for an abonded vehicle title. They gave me the name and address of the last know owner on file. I had to send a certified letter to that address and wait 30 days (for the guy to either reclaim the car, or if they moved; I had to bring the unopened letter with RETURN TO SENDER stamped on it back to DMV). After that, I went in with all my paperwork and got a title in my name. You may not have to file for an abonded title since you have a bill of sale, but you will probbaly will have to go through some process of notifiying the last registered owner to prove to the DMV that he/she sold the car and it isn't stolen. ALSO, some people may not be eager to help out as they might owe taxes on a vehicle they bought or sold and "jumped" the title to another person. I also spoke with my lawyer, and if I was not able to get a title, I had a pretty good chance in court of getting my money back since they were not the "legal" owner of the car in the first place. Anyway, be honest at the DMV, and best of luck!