An innocent bystander was shot and killed at a “No Kings” protest in Salt Lake City on Saturday night. According to the Salt Lake City police, the bystander was mistakenly shot by a self-identified “peacekeeper” at the protest who was associated with the event organizers.

In a city notorious for unruly crowds at large sporting events, protesters were peaceful and law-abiding — as were the police.

Detectives don’t yet know why the alleged rifleman pulled out a weapon or ran from the peacekeepers, but they charged him with murder and accused him of creating the dangerous situation that led to A...