"I don't think it was a question of letting him go," said BWI spokesman Jonathan Dean. He said the gun was detected by screening technology rather than a physical examination of the luggage.
Amy Kudwa, a spokeswoman for the federal Transportation Security Administration, said a baggage inspector saw the firearm in the passenger's luggage about 6:40 a.m. She said the order to evacuate the concourses was given at 7:11 a.m. after attempts to locate the passenger were unsuccessful.
Kudwa said the gun was turned over to the Maryland Transportation Authority Police.
Cpl. Jonathan Green, a police spokesman, said the gun was a loaded Raven Arms MP-25 semiautomatic weapon. He said investigators were working yesterday to determine whether it was registered.
Though the passenger who was carrying the handgun had not been located as of late yesterday, the police will have some advantages in identifying him. Green said the checkpoint is covered by video surveillance, and to reach the checkpoint, the passenger had to go through an identity check to show that he was a ticketed passenger.
According to Green, police did not know whether the passenger boarded a flight or left on foot.
Dean said he could not explain why almost a half-hour elapsed between the detection of the weapon and the evacuation order.
"Shutting down a concourse is something we try to avoid if possible," he said. The evacuation was ordered out of "an abundance of caution," he said.
Passengers were permitted to re-enter the concourses about 8:10 a.m. after police officers and dogs searched the terminals. Dean said operations were restored by 9:30 a.m.
Dean said Southwest Airlines held some flights so that passengers could board. He said he had no estimate of how many passengers might have missed flights as a result to the disruption.
One passenger who didn't fly was Rich Loeffler of Columbia. He said he was waiting in line with two companions at Concourse A about 6:40 a.m. for a 7:50 a.m. flight to Chicago when a commotion broke out near the checkpoint. He said he didn't see the passenger with the handgun but saw police officers rushing to the scene on foot and on motorized scooters.
"The passengers were calm," he said. "People might have been a bit irritated."
Loeffler said the confusion was compounded because passengers couldn't hear the messages airport officials were trying to deliver using small, hand-held megaphones.
"What they could do better at BWI is get a sound system that penetrates," he said.
Loeffler, who works in marketing, said that by the time passengers were allowed to re-enter the concourses, he had missed his chance to make a scheduled business meeting in Chicago.
"It was supposed to be a face-to-face meeting, but sometimes you have to find another way to get it done," he said.