(NewsNation) — More information is coming out about the men who allegedly planned a July 4 mass shooting in Richmond, Virginia, before being thwarted by police.

Police arrested two Guatemalan Nationals, Rolman Balacarcel, 38, and Julio Alvarado-Dubon, 52, and seized multiple assault weapons, and more than 200 rounds of ammunition, at their residence. A tipster, now being called a “hero citizen” by officials, was the one who told authorities they overheard a conversation about an attack on the city’s popular Fourth of July celebration being planned.

“I’m thankful for the hero citizen who called in because they heard something, they heard these two individuals who are potentially plotting to cause mass casualties and mass chaos in the city of Richmond during our Fourth of July fireworks show,” Richmond Mayor Levar Stoney told NewsNation’s “Rush Hour” in an exclusive interview Wednesday.

Balacarcel and Alvarado-Dubon were charged with being non-U.S. citizens in possession of a firearm. More charges are possible. The two men are now being held without bond at a local jail.

Court documents obtained by NewsNation show Alvarado-Dubon is being held on a $15,000 bond. He has lived in Richmond for three years, and before that was in New Jersey, where he was a construction worker. It appears he came to the U.S. legally, according to the documents, but overstayed his visa by four years. Alvarado-Dubon does not have a previous criminal record.

Meanwhile, Balacarcel was arrested in the Charlottesville area and is being held without bond.

U.S. Immigration and Customs Enforcement is involved with the case, but NewsNation did not hear back from the agency about the suspects’ immigration status, or whether there are plans to deport them.

Stoney did not give any more information on the men’s possible motivation for the alleged plot during the “Rush Hour” interview on Wednesday. But Police Chief Gerald M. Smith told NewsNation that the duo’s intent was to conduct a mass shooting.