They had all the records. He bought off GunBroker.com and filled out 4473’s for all of them. How they got him is that a bunch of the guns he bought and sold ended up at crime scenes and in the possession of prohibited persons. Several of them are the witnesses cited in the warrant.
That information is from the ATF? ☺
That was the only place he was buying and selling guns. He was doing it other places also.