The Boston Police Department arrested two gunmen who threatened “violence” at the city’s Pokemon World Championship, the BPD announced Sunday.

Kevin Norton, 18, and James Stumbo, 27, were both arrested and charged with unlawful possession of a firearm on Friday.

The incident began developing on Thursday, when security officers at the Hynes Convention Center—host of the Pokemon World Championships—contacted the Boston Regional Intelligence Center (BRIC) about threats made on social media against attendees.

Norton and Stumbo, who had driven in from Iowa, were stopped from entering the event when officers found several firearms in their car. The pair was unable to provide a license to carry; after being held, they were released.

A search of the vehicle on Friday turned up some disturbing arsenal, including shotgun, a rifle, several hundred rounds of ammunition, and a hunting knife. Norton and Stumbo were arrested Friday night in what city officials hailed as a “great job in the stop and prevention of a potential tragedy.”

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Write to Tanya Basu at tanya.basu@time.com.