Security officials at Louisville International Airport retrieved a firearm from the luggage of a police trainer.
Bob Stewart's handgun was found as he was passing through a security checkpoint on his way to Florida on Feb. 24.
Stewart said he took the gun to work earlier that day to practice at the police firing range. He said he forgot the gun was in his bag because it was hidden underneath other personal items.
Stewart was taken for questioning after the gun was found.
Both the FBI and the Transportation Security Administration are investigating the incident, airport spokeswoman Rande Swann said. Federal authorities have not yet said whether he would be charged.
Stewart has been training the Louisville police force for a year. He served as captain for the Washington, D.C., police and later retired. He also served as chief of police in Ormond Beach, Fla.