The gun dealers weren't in violation of the law either.
Based on the whim of our ruling lords that they cared not for the law at this time.
Since we are a regime ruled by the whim of men, not a free republic governed by the rule of codified law, the law was whatever our rulers declared it to be at that particular second.
Actually, it's because gun sales to foreign nations work under a license structure, which means the dealers aiding in the investigation could receive a license.