little legal advise.
1. as we can all already tell the guy would have been a moron for letting you "test drive" his car and go "sure why dont you take the plasma it like to go for a drive." but either way, he needs proof he owned a plasma.
2. how long ago was the car reported stolen? im sur you would have taken photos of it and if they have a date on them which is before he reported stolen you will have a bit more evidence.
also you have bank reciepts and everything and if you wrote a cheque for him the stub of yours would have had what you bought.
3. you relise you must have a copy of the hand over papers. your case is liekly to get completely looked over for disregarding the proper legal situation. no signed available papers = it was not a legal contract and possibly would not hold up in court.
the legal system is f**ked either way but you may find a loop hole. AND if this was the first car you have bought on your own then you might not go for negligence to insure a legal contract if you did not know the steps involved.
but law is always changing, i am studying law at the moment but not this particuar area. mainly media so you cannot take my full word for this
good luck anyway.