Update: (Remember, this vehicle is already 3 owners away from me.)
Met with the guy I sold it to who signed another bill of sale no problem - stand up guy. So, I'm in the clear.
Get this: The lot wouldn't even let me see the Jeep, because I told them I wasn't the owner over the phone, but they can still hold me liable for the fees, because I'm the last registered owner. Nice catch22 there.
I finally tracked down the current owner, who still knew nothing but that it had been towed. The previous (to him) owner had called him, but gave him some bad info that it had to stay in impound for a month. I gave him the file number and phone number of the impound lot, as well as the bad news that the fees were up to $500. Who has a vehicle towed and doesn't even call the police or city to find out what to do? Goes to auction on Saturday, so he'd better act quick.
Moral of the story, keep your bill of sale and don't tell the lot people too much when you call them!