BOSTON — Police and prosecutors said Monday they thwarted a massacre planned for the Pokemon World Championship held here this weekend.

Boston police arrested James Austin Stumbo and Kevin Norton of Iowa on Saturday “because of threats of violence made over social media.” When police searched Stumbo and Norton’s vehicle parked in a garage several blocks from the Pokemon event, they found a shotgun, an AR-15 assault rifle, a hunting knife, and 250 rounds of ammunition.

Stumbo, 27, and Norton, 18, are charged with unlawful possession of several firearms and unlawful possession of ammunition. Both men are being held without bail pending a dangerousness hearing on September 1.

“We mitigated the threat by intercepting those people,” Suffolk County District Attorney Daniel Conley said at a press conference Monday.

Police Commissioner William Evans said both men on a private Facebook group made references to the Columbine school shooting, Boston marathon bombing, and specific threats against tournament players.

“MY AR-15 says you lose,” Stumbo allegedly wrote online.

The moderator was alarmed enough to tell security at the Pokemon World Championship in Boston where the two men were headed to play in the U.S. masters division. Security detained Stumbo when he tried to enter and then and stopped Norton, too. Both men were slapped with a “No Trespass Order.”

“I think it goes to the whole idea of, if you see something, say something,” Evans said.

Prosecutors said that when Norton learned he was banned from the group for bullying someone, he said: “Oh, ok, that’s fine then I will just shoot him on Friday thanks.”

Stumbo wasn’t exactly shy about his arsenal or his alleged target; he posted a photo of the car and guns in a public Facebook group entitled “Mayhem Pokemon Crew.”

“Kevin Norton and I are ready for Worlds Boston here we come!!!” the caption read before they drove 25 hours to Boston.

“Good luck!” wrote another person.

“With killing the competition?” asked Norton.

“Haha yes,” replied Faux.

Hynes Convention security called the Boston Police Department, which radioed two officers to look into Norton and Stumbo. The “officers were informed” of Stumbo’s post on Facebook, according to police. When Stumbo was questioned, he claimed the Facebook post was taken out of context. However, Norton told police where their car was parked and that it had weapons inside.

Police obtained a warrant on Friday and on Saturday, the two were arrested at a motel in nearby Saugus, Massachusetts, for not having permits to carry the guns and ammo.

The D.A.’s office said Norton and Stumbo are “not currently facing charges in connection with threats each man allegedly made online; the investigation, however, is ongoing.”

The 12th Pokemon World Championship hosted hundreds of players from 30 different countries and thousands more spectators. Winners are given thousands of dollars’ worth of prizes, and $2 million worth of scholarships are donated.

Correction, 8/24/15 7:58 a.m.: A previous version of this article said police found a hunting rifle; it was a hunting knife.