That's not good, but I think this is a case of buyer beware.
Its your responsibility to get the REV check to make sure this kind of thing doesn't happen. (See http://www.revscheck.com.au/what/)
Have the Police got you in trouble or did you just get a warning and need to re-register the car? Obviously, you'll need to register it straight away. Which State are you in?
Do you still have the contact details of the seller? Then you could dob them into the Police as well as try to get some money back.