RICHMOND, Va. (AP) — A tipster who warned police in Richmond, Virginia, about a potential mass shooting on July 4 told police the man who was planning the attack has connections to a drug gang that operates in Mexico and the U.S., according to a search warrant affidavit.

The tipster, who is described as a “concerned citizen” in the affidavit, identified the man planning the shooting as Rolman “Chapin” Balcarcel Ac, 38, one of two men arrested by Richmond police in connection with the alleged plot.

The tipster told police Balcarcel Ac has connections to the Los Zetas criminal syndicate. Detective Michael Kiniry wrote in the affidavit that “Zetas” is a reference to a gang affiliate with operations in Mexico and the U.S.

The tipster also told police that Balcarcel Ac showed him three guns on June 21.

The affidavit was used to obtain a warrant to search a home in Richmond where Balcarcel Ac lived with a second man who was also arrested in connection with the alleged plot, Julio Alvarado-Dubon, 52. It contains no details of the alleged plot, except to say that the tipster told police a mass shooting was planned in Richmond on July 4.

Authorities have said both men are from Guatemala and are in the U.S. illegally. The only charge against them is possession of a firearm by a non-U.S.-citizen, although Richmond police have said they could face additional charges.

During a news conference Wednesday, Richmond police Chief Gerald Smith said the tipster said the attack was planned for the Dogwood Dell Amphitheater, where an annual fireworks show is held. The search warrant application filed Thursday does not mention any specific location for the alleged planned attack.

The announcement from Richmond police that they had thwarted an attack came on July 6, two days after a gunman opened fire from a rooftop during a Fourth of July parade in the affluent Chicago suburb of Highland Park, killing seven people and injuring more than three dozen.

Richmond police have released few details about the alleged plot or said how formulated the plan was when they arrested Alvarado-Dubon on July 1. Balcarcel Ac was not arrested until July 5. They have not identified any motive for the alleged plot.

“It was a very serious threat. Any threat against life and certainly that of a mass shooting is gravely serious. No further information is being provided about this beyond what’s been provided at this stage,” police spokesperson Tracy Walker said in an email Friday.

“The suspect clearly announced a plan to carry this out and clearly had the means to do so based on the weapons and several hundred rounds of ammunition that was seized,” Walker said.

Both men are being held in local jails, Balcarcel Ac in Charlottesville and Alvarado-Dubon in Richmond.

Immigration officials told news outlets that U.S. Immigration and Customs Enforcement has lodged immigration detainers on both men. Detainers are notices that the Department of Homeland Security issues to law enforcement agencies to inform them that ICE plans to take custody of someone who is currently in their custody.

Court documents filed in General District Court in Richmond say Alvarado-Dubon has lived in Richmond for three years and works in the construction industry. The documents say his visa expired four years ago.

The search warrant affidavit says that after police received the tip about a planned mass shooting, they contacted Homeland Security, then went to a home in Richmond, where Alvarado-Dubon answered the door and allowed them to come inside.

Kiniri wrote that police saw two Glock magazines and a rifle round in plain view in the living room. The affidavit said a second man appeared and provided a Colorado identification with the name “Rolman A. Balcarcel AC.” The affidavit said the man had two Colorado driver’s licenses, a Guatemala ID and a Mexico ID. An agent from Homeland Security Investigations determined that both men are in the U.S. illegally and that Balcarcel Ac has had two previous deportations, the affidavit states.

Alvarado-Dubon’s attorney, Jose Aponte, did not immediately return a call seeking comment Friday. No attorney is listed on court documents for Balcarcel Ac.

Police said Wednesday that officers seized two assault rifles, a handgun and hundreds of rounds of ammunition from the home.

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