BOSTON - Two men from Iowa made online threats against Pokemon competitors -- referring to the Boston Marathon bombings and the Columbine High School massacre -- then drove 25 hours to Boston, where they were stopped as they tried to register for the World Pokemon Championships, police said Monday.

Kevin Norton, 18, of Ames, Iowa, and James Stumbo, 27, of Boone, Iowa, were ordered held without bail on gun charges Monday pending a dangerousness hearing scheduled for Sept. 1.

Lawyers for the men did not immediately return calls seeking comment.

Boston police Commissioner William Evans said the men made threatening statements in a closed online Pokemonforum and on other social media before driving to Boston for the competition. Both were experienced players invited to attend the event at the Hynes Convention Center.

The moderator of the Pokemon forum notified security at the convention center, then Hynes officials notified police, Evans said. The two men were stopped as they entered the convention center Thursday and were detained for questioning.

Police seized their car, which they believed they had guns and ammunition, but they released the men as they waited for a search warrant, Evans said. Norton and Stumbo were arrested Saturday morning at a hotel in Saugus, just north of Boston.

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Officers found a 12-gauge shotgun, an AR-15 rifle, several hundred rounds of ammunition and a hunting knife in their car, police said. They said neither man was able to produce a gun license.

Evans said police are not sure exactly what they intended to do, but believe they posed a "serious threat" to the people at the competition.

"Inside, there were a lot of kids, a lot of gamers ... thank God we were able to cut off whatever these two individuals coming from Iowa were up to," Evans said during a news conference.

In a Facebook chatroom conversation involving several people, Stumbo referred to his AR-15 rifle, stating, "MY AR-15 says you lose," prosecutors said. They said Stumbo acknowledged posting, "Kevin Norton and I are ready for worlds Boston here we come!!!" as the caption below a picture of Norton's car with the AR-15 and shotgun displayed on its trunk.

The Boston Police Department released this photo via Faceboo of a 12-gauge Remington shotgun, a DPM5 Model AR-15 rifle, several hundred rounds of ammunition, and a hunting knife recovered by detectives on Aug. 21, 2015. Photo Credit: Facebook

Prosecutors also said Norton, when barred from accessing a chatroom that he was banned from for bullying another person, stated, "Oh, ok, that's fine then I will just shoot him on Friday thanks."

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Players from more than 30 countries competed at the three-day, invitation-only event for a share of more than $500,000 in scholarship awards, including $10,000 for each Pokemon Video Game World Champion and $25,000 for each Trading Card Game World Champion.

Norton's Facebook page includes a photo of him firing a handgun. It says he attended Ames High School from 2011 to 2015 but doesn't specify if he graduated. A spokeswoman for the school said she could not release any details under student privacy laws.

Norton also lists Fareway grocery store as a workplace. An assistant manager who answered the phone at one of two Fareway stores in Ames declined to comment on Norton or give details of his employment.

Boston Police Superintendent Paul Fitzgerald, chief of the Bureau of Intelligence and Analysis, said authorities do not know what motivated the men.

"They made references, but they were pretty obvious references -- bullet holes and bombings and that kind of thing," he said.

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Norton and Stumbo are not currently facing charges for the threats they allegedly made online. Police said the investigation is continuing.

"Due to quick action, the potential threat was resolved," the Pokemon Company International said in a statement. "The Pokemon Company International takes the safety of our fans seriously and will continue to ensure proper security measures are a priority."