Prosecutors on Thursday dropped charges against an American man arrested in March for alleged possession of a firearm after bringing a handgun and ammunition in his luggage into Japan and passing through airport customs undetected.

Prosecutors did not provide a reason for not indicting the 73-year-old man. Local police said he arrived at Kansai airport in Osaka Prefecture on a flight from Hawaii on March 22.

The following day, he realized the revolver loaded with three bullets was in a bag in his suitcase.

He reported the discovery to an attendant as he was boarding a cruise ship in Kobe later the same day and was arrested on March 24.

The case highlighted concerns over screening measures during the World Exposition opening in the city of Osaka. Many international arrivals are expected during the event lasting six months from April 13.