Guns to NYC
The guns were being sold in New York. As a part of a sting by NYPD they were watching these guys. What they could not figure out was how the guns were getting to New York. The police figured they were being driven up I-95 by a courier. Eventually the penny dropped when they realized the guy worked for Delta and was carrying the iron himself.
If it was not for the NYPD this would never have come to light. It was not the TSA or anything to do with the airlines that busted the guy(s).