Had it happen to a friend of mine. He sold a shotgun, than over the years changed hands a few times and ended up used in a robbery. The cops came looking for him, and he had to explain and try to prove that he sold the the gun years ago.
If you sell, document it. Or use a FFL to transfer.
Do we really want to be on the slippery slope towards confiscation?
Just because you owned a gun once that was later used in crime – years later, doesn’t mean you are responsible for that crime.
Should we have to document the purchase and sale of all of our personal belongings as a hedge against them turning up later at a crime scene?