An Iraq war veteran who was grappling with mental health issues opened fire at Fort Hood, Texas, in an attack that left four people dead and 16 wounded Wednesday afternoon, according to preliminary law enforcement and military reports. The gunfire sent tremors of fear across a sprawling Army base still reeling from one of the worst mass shootings in US history.
Many basic details about the shooting remained unclear in the chaotic hours after the first calls for help around 4 p.m., but senior law enforcement officials said the shooting did not appear to be linked to any foreign terrorist organizations. The shooter was among those who died, the officials said.
The officials identified the shooter as Army Specialist Ivan Lopez, 34, a military truck driver, who was dressed in his standard-issue green camouflage uniform. Lopez opened fire in two locations on the vast central Texas post, inside a building housing the First Medical Brigade and in a facility belonging to the 49th Transportation Battalion.
Police spent Wednesday night searching his apartment in Killeen, the city that abuts the base. General Mark Milley, the commander of Fort Hood, said the soldier, whom he did not identify by name, served four months in Iraq in 2011.
Milley said the shooter had behavioral health and mental health issues. He said the soldier, who self-reported a traumatic brain injury and was taking antidepressants, had been under examination to determine whether he had post-traumatic stress disorder.
‘‘We are digging deep into his background,’’ Milley said.
Milley said the soldier opened fire with a .45-caliber Smith & Wesson semiautomatic pistol that was purchased recently but was not authorized to be brought on the base. He was eventually confronted by a female military police officer. He put his hands up but then pulled a gun from under his jacket.
‘‘She engaged,’’ Milley said, then the soldier put the gun to his head and shot himself.
The shooting was the third major gun attack at a US military installation in five years, leaving the nation grappling with the prospect of yet more flag-draped funerals for troops killed on the homefront. A government contractor went on a shooting rampage at the Washington Navy Yard in September, leaving 12 people dead. And in 2009, Army Major Nidal Hasan opened fire on a group of soldiers at Fort Hood preparing to deploy to Iraq and Afghanistan, killing 13 people and wounding more than 30.
President Obama said he was heartbroken. Speaking during a fund-raising trip to Chicago, he pledged to get to the bottom of what happened.
Although bases such as Fort Hood contain large storehouses of armaments, and many of their inhabitants have spent years at war, military posts are usually among the most idyllic communities in the country, a throwback to the 1950s, with manicured lawns, drivers who conscientiously abide by the speed limit and parents unafraid to allow their children to frolic out of sight.
After the Washington Navy Yard shooting, Defense Secretary Chuck Hagel ordered a series of security changes at military installations, including more rigorous screening of personnel and the creation of an analysis center to examine internal threats.
‘‘When we have these kinds of tragedies on our bases, something’s not working,’’ he said Wednesday evening during a visit to Hawaii. ‘‘We will continue to address the issue. Anytime you lose your people to these kinds of tragedies, it’s an issue, it’s a problem.’’
Genera; Martin Dempsey, the chairman of the Joint Chiefs of Staff, said that many questions remained about the shooting, but that a principal initial focus was to support the victims and their families.
‘‘This is a community that has faced and overcome crises with resilience and strength,’’ he said in a statement.
Soldiers based at Fort Hood were called upon, often repeatedly, to deploy to Iraq and Afghanistan over the past decade. Those combat tours have exacted a profound physical and emotional toll on many of them. Others have rebounded and are continuing their military careers or are transitioning into the civilian world.
Dozens of ambulances and law enforcement vehicles converged on the scene after the shooting. Several of the wounded were transported to a hospital on the base.
The base was placed on lockdown for much of the afternoon, with loudspeakers across the facility urging people to shelter in place. The order applied to thousands of families that live on the post. It was lifted in the early evening, once law enforcement authorities had determined that a sole gunman was responsible for the shooting.
With the exception of military police officers, soldiers at Fort Hood and all other US military installations are not armed or permitted to carry privately owned firearms. The restrictions on personal weapons were expanded following the 2009 massacre and an epidemic of suicides at Fort Hood, the largest active-duty armored post in the country. Current policy requires soldiers to register their personal weapons with their commanders and to keep those weapons in a secured room.
Hasan was convicted of multiple counts of murder last year and sentenced to death.
The shootings exposed a number of failings by the Defense Department, which a Pentagon report concluded was unprepared for internal threats.
Among those on the base Wednesday was Matt Lausch, the chief of the Manassas, Va., volunteer fire department. He was working on his company’s contract to build a hospital on the grounds when the alert system warned the base to ‘‘seek shelter immediately.’’
Lausch, who remained in a construction trailer, said a flood of emergency personnel could be seen and heard streaming across the base.
‘‘There was a huge, huge response by police and first responders,’’ Lausch said. He and co-workers learned of the shooting from social media feeds once they locked themselves in the trailer.