Transportation Security Administration agents found a loaded 9 mm handgun tucked in the pocket of a messenger bag after a passenger carried the gun into a security checkpoint Tuesday afternoon.

The firearm was spotted by a TSA agent using an X-ray machine. The gun’s owner, a man from Poland, Maine, said he forgot he had the loaded gun with him when he entered the airport.

TSA agents found the handgun had a round chambered and 12 cartridges loaded in a magazine, along with a loaded spare magazine also containing 12 rounds.

Poland, Maine, man caught by #TSA with his 9 mm handgun loaded with 12 bullets, including one in the chamber, this afternoon at the @portlandjetport checkpoint. He claimed that he forgot he had his loaded gun and extra loaded magazine with him in his messenger bag. pic.twitter.com/nzTCOnZtPo

— TSA Northeast (@TSA_Northeast) December 10, 2019

After the firearm was found, Portland police responded and questioned the man, who was not identified. Police returned the handgun to him, and he secured it in his vehicle and was allowed to catch his flight, the TSA said.

This is the third gun found at the jetport this year. The other two loaded guns were seized less than two months ago, on  Oct. 31 and Nov. 1.

Passengers are permitted to travel with firearms, but only if they are properly packaged in checked baggage and declared. Guns must be unloaded, packed in a hard-sided case, locked and packed separately from ammunition.

Across the country, TSA agents seized 4,239 firearms from carry-on bags in 2018.

Bringing a firearm to a TSA checkpoint can be charged criminally, and TSA has the power to assess civil fines of up to $13,333 for weapons violations. A typical first offense carries an average penalty of $4,100, according to the agency.