Gunfire erupted Saturday night at a “No Kings” protest in Salt Lake City, Utah, killing an innocent bystander, cops say.

According to the Salt Lake City Police Department, about 10,000 people came downtown as part of a nationwide protest opposing President Trump’s military parade in Washington D.C. and his policies.

Shortly before 8 p.m. cops heard a volley of shots, sending panicked demonstrators fleeing for safety in parking garages and local businesses. Officers found a man, later identified as 39-year-old Arthur Folasa Ah Loo, who had been shot. First responders tried saving Ah Loo, but those efforts were unsuccessful and he died.

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Witnesses then pointed out to a man dressed in a black clothing and wearing a mask who was crouched among a group of protesters and suffering from a gunshot wound. Nearby was an AR-15-style rifle that he had been allegedly holding. Cops identified him as 24-year-old Arturo Gamboa.

Cops also detained two men wearing neon vests who were apparently part of the event’s peacekeeping team.

The peacekeepers said they saw Gamboa move away from the crowd and behind a wall, which they found suspicious. Then they allegedly saw Gamboa pull out the rifle from his backpack. They ordered him to drop the weapon, but instead witnesses said he “began running toward the crowd gathered on State Street, holding the weapon in a firing position,” cops wrote.

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That’s when one of the peacekeepers allegedly fired three shots. One hit Gamboa, while they other hit Ah Loo, cops said.

“Detectives have not been able to determine, at this time, why Gamboa pulled out his rifle and began to manipulate it or why he ran from the peacekeepers when they confronted him,” cops wrote.