The shooter apparently walked into a building and began firing a .45-caliber semi-automatic pistol. He then got into a vehicle and continued firing before entering another building.
He was eventually confronted by military police in a parking lot. As he came within 20 feet of an officer, the gunman put his hands up but then reached under his jacket and pulled out his gun. The officer drew her own weapon, and the suspect put his gun to his head and pulled the trigger a final time, according to Lt. Gen. Mark A. Milley, senior officer on the base.
The gunman, who served in Iraq for four months in 2011, had sought help for depression, anxiety and other problems. Before the attack, he had been undergoing an assessment to determine whether he had post-traumatic stress disorder, Milley said.
The married suspect had arrived at Fort Hood in February from another base in Texas. He was taking medication, and there were reports that he had complained after returning from Iraq about suffering a traumatic brain injury, Milley said. The commander did not elaborate.
The gunman was never wounded in action, according to military records, Milley said.
There was no indication the attack was related to terrorism, Milley said.
The military declined to identify the gunman until his family members had been notified. Texas Rep. Michael McCaul, chairman of the House Homeland Security Committee, said he was named Ivan Lopez but offered no other details.
The weapon had been purchased recently in the local area and was not registered to be on the base, Milley said.
Late Wednesday, investigators had already started looking into whether Lopez's combat experience caused lingering psychological trauma. Among the possibilities they planned to explore was whether a fight or argument on the base triggered the attack.
"We have to find all those witnesses, the witnesses to every one of those shootings, and find out what his actions were, and what was said to the victims," said a federal law enforcement official, speaking on condition of anonymity because he was not authorized to discuss the case by name.
The official said authorities would begin by speaking with Lopez's wife and expected to search his home and any computers he owned.
The injured were taken to the base hospital and other local hospitals. At least three of the nine patients at Scott and White Hospital in Temple were listed in critical condition.
Wednesday's attack immediately revived memories of the shocking 2009 assault on Fort Hood , which was the deadliest attack on a domestic military installation in U.S. history. Thirteen people were killed and more than 30 wounded.
Until an all-clear siren sounded hours after Wednesday's shooting began, relatives of soldiers waited anxiously for news about their loved ones.
"The last two hours have been the most nerve-wracking I've ever felt," said Tayra DeHart, 33, who had earlier heard from her husband that he was safe but was waiting to hear from him again.
Brooke Conover, whose husband was on base at the time of the shooting, said she found out about it while checking Facebook. She immediately called her husband, Staff Sgt. Sean Conover.
"I just want him to come home," Conover said.
President Barack Obama vowed that investigators would get to the bottom of the shooting.
In a hastily arranged statement in Chicago, Obama reflected on the sacrifices that troops stationed at Fort Hood have made — including enduring multiple tours to Iraq and Afghanistan.
"They serve with valor. They serve with distinction, and when they're at their home base, they need to feel safe," Obama said. "We don't yet know what happened tonight, but obviously that sense of safety has been broken once again."
The president spoke in the same room of a steakhouse where he had just met with about 25 donors at a previously scheduled fundraiser for the Democratic National Committee.
The November 2009 attack happened inside a crowded building where soldiers were waiting to get vaccines and routine paperwork after recently returning from deployments or preparing to go to Afghanistan and Iraq.
Army psychiatrist Nidal Hasan was convicted and sentenced to death last year in that mass shooting. He said he acted to protect Islamic insurgents abroad from American aggression.
According to testimony during Hasan's trial last August, Hasan walked inside carrying two weapons and several loaded magazines, shouted "Allahu Akbar!" — Arabic for "God is great!" — and opened fire with a handgun.
The rampage ended when Hasan was shot in the back by Fort Hood police officers. He was paralyzed from the waist down and is now on death row at the military prison at Fort Leavenworth in Kansas.
After that shooting, the military tightened security at bases nationwide. Those measures included issuing security personnel long-barreled weapons, adding an insider-attack scenario to their training and strengthening ties to local law enforcement. The military also joined an FBI intelligence-sharing program aimed at identifying terror threats.
In September, a former Navy man opened fire at the Washington Navy Yard, leaving 13 people dead, including the gunman. After that shooting, Defense Secretary Chuck Hagel ordered the Pentagon to review security at all U.S. defense installations worldwide and examine the granting of security clearances that allow access to them.
Asked Wednesday about security improvements in the wake of the shootings, Hagel said, "Obviously when we have these kinds of tragedies on our bases, something's not working."