Salt Lake City police say a demonstrator who was shot at the city's “No Kings” protest has died and that the bullet that killed him appears to have been fired by one of the demonstration's peacekeepers.

A man who was believed to be part of a peacekeeping team for the “No Kings” protest in Salt Lake City shot at a person who was brandishing a rifle at demonstrators, striking both the rifleman and a bystander who later died at the hospital, authorities said Sunday.

Police took the alleged rifleman, Arturo Gamboa, 24, into custody Saturday evening on a murder charge, Salt Lake City Police Chief Brian Redd said at a Sunday news conference. The bystander was Arthur Folasa Ah Loo, 39, a fashion designer from Samoa.

Detectives don’t yet know why Gamboa pulled out a rifle or ran from the peacekeepers, but they accused him of creating the dangerous situation that led to Ah Loo’s death. The Associated Press did not immediately find an attorney listed for Gamboa or contact information for his family in public records.