A gunman who killed three people and injured seven others at an In-N-Out restaurant in Twin Falls, Idaho, died from a self-inflicted gunshot wound, police said.

Authorities identified the suspect as 24-year-old Chad Williams and said they believe he acted alone.

An off-duty state trooper and an armed citizen fired back and helped divert the shooter, preventing further casualties.

Investigators are still working to determine a motive, while the suspect’s family is cooperating with police, the AP has reported.

Officials also warned the public about false information online incorrectly naming another person as the shooter.