TWIN FALLS, Idaho (AP) — The suspect in a fatal weekend shooting at an In-N-Out Burger restaurant in southern Idaho died of a self-inflicted gunshot wound, police said Sunday.

Investigators are confident that 24-year-old Chad Williams acted alone during the shooting Saturday in Twin Falls, Police Chief Matthew Hicks said at a news conference. In all, three people died and seven others were injured at the recently opened restaurant.

Authorities said two of the injured were treated at a hospital and released, three were listed in stable condition and two were in critical condition.

Hicks said an off-duty state trooper and an armed citizen both fired back and diverted the gunman. “We believe their actions helped drive the suspect away from the scene, preventing further casualties,” the chief said.