Was the LEO speaking of handguns? There was a burglary in my area where handguns were stolen and within 24 hours used in a crime in an adjacent state. I can see handguns being resold, but long guns are another story. They go missing in airports.I'm not sure of that with regard to thieves. I say that as someone who has had firearms stolen in a break-in.
From my discussions with law enforcement, firearms are like cash. A sheriff's deputy in charge of returning stolen goods told me when I had some of my guns returned that he knew of firearms that had switched hands a dozen times within 24 hours.
Of course, thieving airline or airport employees may be a different sort of thief.