When a FFL dealer, C&R , etc. gives up his license his records (bound book) must be sent to ATF. They have people putting these records into a computer data base. They also have records of new guns from factory to dealers. So they find a gun at a crime seen, go to maker, get dealers name and then go to the dealer. Yes, we have a national registration, its just not direct. The original law sated that the records could not be put into a data base, either that's changed or they are ignoring the law.
You can never go home again.