Two Iowa men whom police say planned a mass shooting at the Pokémon World Championships in Boston were ordered held without bail Monday. A dangerousness hearing is set for Sept. 1.

Kevin Norton, 18, and James Stumbo, 27, who were invited to participate in the weekend tournament, were arrested Saturday on firearms charges after police were alerted to alleged threats they'd made to the event through social media.

“We can never read someone’s mind,” The Boston Globe quotes Police Superintendent Paul A. Fitzgerald as saying. “What we can read is what they were saying and the actions that they took, bringing the weapons they were showing online as a threat.”

“That could have been a mass shooting,” he added, noting the involvement of Boston’s Joint Terrorism Task Force, which includes federal agents. "So obviously the federal agencies were concerned with that.”

After both men were barred from entering the Hynes Convention Center on Thursday, police spoke with the two and obtained a search warrant for Norton’s 2002 Chevy Prizm and discovered a 12-gauge Remington shotgun, a DPM5 Model AR-15 rifle, hundreds of rounds of ammunition and a hunting knife. Norton and Stumbo were then arrested Saturday morning at their motel in Saugus, north of Boston.

Stumbo last week allegedly posted a photo to the Mayhem Pokemon Crew Facebook page of two guns on the trunk of a car, with the message, “Kevin Norton and I are ready for worlds Boston here we come!!!” When another poster wished them “Good luck,” Stumbo responded, “With killing the competition?”

According to prosecutors, when Norton was banned from an online chat room for bullying, he allegedly replied, “Oh, ok, that’s fine then I will just shoot him on Friday thanks.” Both men had allegedly made threats against individuals and discussed mass shootings in chat rooms.

Norton and Stumbo face charges of unlawful possession of a firearm, unlawful possession of ammunition and unlawful possession of a large capacity rifle. Although they've not been charged in connection with any threats they allegedly made online, the Suffolk County District Attorney's Office noted that the investigation is ongoing.