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

The Salt Lake City Police Department reported that roughly 10,000 individuals gathered downtown for a nationwide protest against President Trump’s military parade in Washington D.C. as well as his policies.

Just before 8 p.m., officers heard a series of gunshots, causing panic among protestors who scrambled for cover in parking garages and nearby businesses. They discovered a man, 39-year-old Arthur Folasa Ah Loo, who had been shot. First responders attempted to save Ah Loo, but unfortunately, he passed away.

Love true crime? Sign up for our newsletter, The Law&Crime Docket, to get the latest real-life crime stories delivered right to your inbox.

Witnesses then directed officers to a man in black clothing and wearing a mask who was crouched among a group of demonstrators and suffering from a gunshot wound. Close by was an AR-15-style rifle which he was allegedly holding. Police 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.

More from Law&Crime: ‘Absolute vile piece of s—’: Wife of state senator used ‘body as a shield’ to protect couple’s daughter from assassination attempt suspect, nephew says

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.