if you bought a car that was stolen, found out it was stolen, took it back to the seller and said "give me my money back or i'll tell dibble" thats only going to get stolen stuff back into circulation

as hard as it sounds, you need to fully co operate with plod to make sure you get out of this with just a hole in your wallet
with electonic goods now, everything is traceable, and shopping the seller (ok, it's not exactly going to be pointing the finger and saying "there is he mr elderly william, and i'm sure you'll find a whole warehouse full of shady mechandice with dubious history" but at least you can say you are doing your bit, tell them who you bought it from, the circumstances they sold it to you under and how much you paid for it etc etc and just hope that it's all a misunderstanding

hope everything works out for the best, in that you get your money back and everything gets cleared up without getting unsociable