The original buyer buys from an FFL and filled out a yellow form. That form stays with the FFL. When the fire arm is associated with a crime, the SN is traced from the manufacturer to the dealer who then provides the LE agency with the yellow form buyer information. This buyer is the next stop in their investigation.Private sales in AZ doesnt require any paperwork so if a person were to sell a gun to another person. And the buyer gets in trouble, how does that gun come back to the previous seller since there is no paper trail? jim