Just got word today..and I want to emphasize that this is not confirmed or yet established fact and may very well be incorrect supposition but:
Apparently, the firearm was in his roll-aboard which he lawfully checked through to his home base and he had acquired the weapon in Buffalo from a friend or relative. It was actually not loaded but had a fully loaded speed loader in the bag with it. The ticket agents were aware and proper procedures were followed. But the TSA realizing it was a crew bag and that the Captain would have access to this bag once loaded objected to the bag going on the aircraft and gave the captain a choice, either you or the firearm, not both are going on the plane. The Captain then got into a heated confrontation over TSA doing what they do best and just making up rules as they go along and was eventually escorted off the premises under arrest.