An "innocent bystander" at the "No Kings" demonstration in downtown Salt Lake City was shot and killed Saturday, police said.
Arthur Folasa Ah Loo, 39, of Utah, died in a hospital, Salt Lake City police said in an update.
Detectives believe Ah Loo was at the demonstration as a bystander and "was not the intended target of the gunfire."
Police have arrested Arturo Gamboa, 24. He was booked into the Salt Lake County Metro Jail on a murder charge. It was not immediately clear whether Gamboa was still in jail Sunday and whether he has an attorney.
Also detained Saturday were two men who were part of the event "peacekeeping team." One of the "peacekeepers" fired the shot that fatally injured Ah Loo, police said.
It was not immediately clear whether those two men will face charges.
The men told police they saw Gamboa move away from the crowd and begin manipulating an AR-15-style rife, prompting them to draw their guns and order him to drop the weapon, police said.
Instead, Gamboa ran into the crowd, holding his gun in "a firing position," police said. In response, one of the "peacekeepers" fired three shots, one of which struck Gamboa and another which hit Ah Loo, according to police.
Police said they are still investigating, specifically looking into the actions of the "peacekeepers," who are not law enforcement officials. Officials still do not know why Gamboa pulled out the rifle or why he ran from the "peacekeepers."
Gamboa did not fire the shot that fatally struck Ah Loo, but he still faces the murder charge because detectives "developed probable cause that Gamboa acted under circumstances that showed a depraved indifference to human life, knowingly engaged in conduct that created a grave risk of death and ultimately caused the death of an innocent community member," police said.
The state medical examiner's office will determine Ah Loo's official cause and manner of death.
A police motor squad detective reported hearing gunshots at 7:56 p.m. Saturday, police said. Officers found Ah Loo injured as they were working to clear the scene and identify the origin of the gunfire, police said.
Officials tried to save the man at the scene before he was sent to the hospital in an ambulance.
Minutes later, police said, they found Gamboa, who was crouching amid a group of people and had a gunshot wound himself. He had an AR-15-style weapon nearby, police said.
Officers also found a gas mask, black clothing and a backpack nearby, the police department said.
They then identified the "peacekeepers" wearing high-visibility neon green vests and carrying handguns.
The march was one of many "No Kings" events throughout the country Saturday, a counter to President Donald Trump's military parade in Washington.
It also came on the heels of days of protests in Los Angeles and other cities across the country following immigration raids.
