Investigators are confident that the gunman, identified as 24-year-old Chad Williams, acted alone during the shooting on Saturday at an In-N-Out location in Twin Falls, Police Chief Matthew Hicks said at a news conference.
In all, four people died, including Williams, and seven others were injured at the recently opened restaurant in the southern Idaho city of about 56,000 people.
Authorities said two of the injured were treated at a hospital and released, three were listed as stable, and two were in critical condition.
Police who responded to the shooting found the body of the suspected gunman in an area near the restaurant.
Hicks said an off-duty state trooper and an armed citizen — whose identities were not immediately disclosed — both fired back and diverted the gunman from the restaurant.
“We believe their actions helped drive the suspect away from the scene, preventing further casualties,” the chief said. “We want to take a moment and commend the actions of the off-duty officer and the citizen, and their heroic action to stop this incident.”
Hicks said detectives are working to determine Williams’ motives, and said the suspect’s family was cooperating fully with law enforcement. Officials asked potential witnesses or anyone with information to contact police.
The chief also warned of misinformation spreading online identifying a different man as the shooter, saying that person had “no involvement in this incident whatsoever.”
One of those killed was an employee, the fast-food chain’s owner said.
The FBI has encouraged the public to submit images and videos related to the shooting.
