Three people were killed and at least two others injured after a gunman opened fire at a crowded In-N-Out restaurant in Idaho, triggering an apparent exchange of gunfire with an armed bystander.

The attack unfolded at around 2:30pm on Saturday in Twin Falls, approximately 130 miles (210km) southeast of Boise. The restaurant had opened only about a week earlier and was packed with customers in one of the city’s busiest commercial districts.

The shooting apparently began inside the restaurant before spilling into the surrounding area, according to footage showing terrified customers and employees fleeing into the parking lot and onto the road as shots rang out.

Video circulating online shows a man armed with an AR-style rifle and dressed in a black shirt and jeans walking out of the venue as the crowd flees. He then approaches a white car, opens its trunk and reaches inside.

In another clip, the suspect is seen walking through a parking lot near a Tesla charging station and firing several shots.

Separate footage appears to show another man firing a pistol toward the rifleman. Eyewitness Lane Koehn, 34, also told the Associated Press that he saw a man with a handgun open fire after the suspected attacker emerged from the drive-through carrying the rifle.

Police have neither confirmed that the pistol-wielding man was a civilian attempting to stop the attack nor established what role his gunfire played. Authorities have also declined to say how the suspected shooter died, leaving open the possibility that he was killed during the apparent exchange.

Koehn said the rifleman fired at least three or four rounds, although he could not tell whether anyone in particular was being targeted. Moments later, he saw an In-N-Out employee drag a wounded female colleague across the parking lot. The woman had apparently been shot in the chest. Koehn, the employee and the pistol-wielding man remained with her until paramedics arrived.

Police sealed off surrounding roads and temporarily closed the Perrine Bridge over the Snake River Canyon. Nearby shops and the Magic Valley Mall were placed under lockdown while officers searched the area and interviewed hundreds of potential witnesses.

Twin Falls Police Chief Matthew Hicks later confirmed that the suspected gunman was among the three people killed.

“We believe the threat to the community is over,” Hicks said, describing the site as an “exceptionally chaotic scene.”

The identities of those killed and injured have not been released. Police are still working to identify the suspected attacker and determine his motive, while the FBI and federal firearms investigators are assisting with the investigation.