A soldier who was being evaluated for post-traumatic stress disorder opened fire at Fort Hood on Wednesday, killing three people and wounding 16 before being engaged by an MP and killing himself, the authorities said. The shooting set off a huge police response and shut down the sprawling Army base, the same facility where a deadly rampage by an officer resulted in 13 deaths in 2009.

Fort Hood’s commanding general said the gunman, an Army specialist who had served in Iraq and was being treated for behavioral and mental health issues, had died of a self-inflicted gunshot wound. The commander, Lt. Gen. Mark A. Milley, told reporters that the soldier’s motive remained unclear, but that the shooting did not appear to be related to terrorism. 

The authorities said Specialist Lopez appeared to have walked into one building, then gone inside a vehicle and fired shots from the vehicle with a .45-caliber Smith & Wesson semiautomatic pistol that had recently been bought in the Killeen area. He got out of the vehicle, walked into another building and opened fire again, and then engaged with a female military police officer before shooting himself.

He put his hands up, General Milley told the New York Times, then reached under his jacket. The female officer pulled out her weapon, and then Specialist Lopez put his weapon to his head and fired. General Milley described the officer’s actions as “clearly heroic,” adding: “She did her job. She did exactly what we would expect of U.S. Army military police.”