RICHMOND, Va. - Only two days after seven people were killed during Independence Day celebrations in Highland Park, Illinois, a Virginia police chief announced an anonymous tip submission potentially saved several lives on the same day.

Police said a caller, whose name was not released, called to say they overheard a conversation on July 1 at a local amphitheater discussing a planned mass shooting. An investigation was rapidly launched, involving the Richmond Police, the U.S. Department of Homeland Security, and the FBI. 

Later that day, police executed a search warrant on a local residence and seized two assault rifles, 223 rounds of ammunition, and the two men who were allegedly having the conversation that the tipper overheard.

The investigation revealed the men were planning a mass shooting during the city's Independence Day celebration.

"There's no telling how many lives this hero citizen saved from one phone call," the Richmond Police Chief said. "Public safety is a responsibility of us all. One phone call saved numerous lives on the Fourth of July."

The suspect, Julio Alvarado-Dubon, 52, was taken into custody and charged with possessing a firearm as a non-U.S. citizen.

Police surveilled Alvardo's roommate, identified as Rolman Balacarcel, 38, for several days before he was arrested on Tuesday in Albemarle County, Virginia, on the same charge. Additional charges could be possible for both suspects, Smith said.

Both men were arrested and are being held in a local jail without bond.