KILLEEN, Texas (CNN) -- Fort Hood.
The name has been seared in our collective memory since a soldier went on a deadly shooting spree there in 2009.
On Wednesday, it happened again.
Specialist Ivan Lopez went from one building at the sprawling Texas military base to a second, firing a .45 caliber handgun -- killing three people and wounding 16 more.
Then the 34-year-old Iraq vet put the gun to his head and pulled the trigger, ending his life and taking with him the reasons for his action.
Authorities are downplaying terrorism -- although they haven't ruled it out until the investigation is complete.
"There are initial reports there may have been an argument in one of the unit areas," Lt. Gen Mark Milley, the post's commanding general, told reporters late Wednesday.
Officers picked up Lopez' wife at their apartment near the base in Killeen, and she was cooperating with law enforcement, an FBI official told CNN.
The man, whom a neighbor said often gave her a friendly wave, was plagued by multiple mental health issues.
Lopez was new on the base, having only arrived there in February. He, his wife and their small daughter moved into their apartment a little more than a week before the shooting.
They were a normal couple, said neighbor Xanderia Morris. "They would smile whenever they'd see someone," she said.
But behind Lopez' smile lay intense emotional torment -- of depression, anxiety and other psychiatric disorders. He was receiving treatment and medication, Milley said.
He served for four months in Iraq in 2011. And while army records don't show him as having been wounded there, Lopez himself reported that he had suffered a traumatic brain injury, Milley said.
He was undergoing diagnosis procedures for Post-Traumatic Stress Disorder (PTSD).
"He was not diagnosed, as of today, with PTSD," Milley said.
Arriving at the diagnosis of the mental ailment that plagues so many war veterans takes time.
Brought a gun
Lopez carried out the killings with a privately owned gun -- a .45 caliber Smith and Wesson semiautomatic pistol he purchased after arriving in Killeen.
When he took it onto the base, he was breaking the rules.
"If you have weapons and you're on base, it's supposed to be registered on base," Milley said. "This weapon was not registered on base."
In addition, people are not allowed to walk around with guns on a military base. They are required to store them in a secured armory.
Sequence of events
The exact sequence of events is not entirely clear. But around 4 p.m., Lopez walked into a building at the base and opened fire. He then got into a car, fired from the vehicle, walked into another building and fired again.
He killed three and wounded 16 -- all of them were army personnel.
Three of the wounded remained in critical condition early Thursday morning.
Authorities could not say whether Lopez knew his victims.
The shootings took place in the medical brigade and the transportation battalion buildings. Lopez was assigned to the 13th sustainment command, which deals with the logistical responsibilities for the post.
The spree went on for about 15 to 20 minutes, Milley said.
The base housing more than 45,000 soldiers and nearly 9,000 civilian employees went on lockdown.
People were told to shelter in place.
Pvt. Dehlan Kay stayed in his barrack, as sirens went off.
"I'm doing good," he told CNN's Wolf Blitzer. "I'm just a little nervous on what's happening."
The all-clear wouldn't go out for another six hours.
A horrifying revelation
At the Lopez apartment, his wife was watching reports of the shooting on TV.
She came out crying, said Morris, the neighbor.
"I'm just worried, I'm just worried," Lopez' wife told her. She hadn't heard from her husband all afternoon.
"I tried to console her and comfort her, let her know everything was OK," Morris said.
They had no idea who the shooter was at the time.
Then, a local TV station identified the gunman as Lopez.
The wife became "hysterical," Morris said.
Ending his life
It took law enforcement about 15 minutes to respond to the gunfire, Milley said.
An officer confronted Lopez in a parking lot.
He reached under his jacket for his pistol, and put it to his head. He fired. Death by self-inflicted gun shot wound.
"It was clearly heroic what she did," Milley said of the offier. "She did her job and she did exactly what we would expect of the U.S. military police."
The last mass shooter
Here, Lopez' actions differed from Fort Hood's last mass shooter.
Army Maj. Nidal Malik Hasan survived after killing 13 people and injuring another 32 on November 5, 2009.
The former military psychiatrist openly told a court that he was on a terrorist mission.
During a hearing in June he said that he fired at soldiers preparing to deploy to Afghanistan to protect leading members of the Taliban.
Hasan was convicted of premeditated murder, and a military jury recommended that he be put to death.
Reporters prodded Milley about the 2009 shooting and Lopez' rampage -- a repeat tragedy.
he would not entertain the notion.
"My reaction was not 'not again here,'" he said. "My reaction was to immediately make sure we had a read on the casualties. Immediately secure the site. Immediately look for one or more shooters."
But others were more introspective.
"Tonight, Texans' hearts are once again very heavy. The scenes coming from Fort Hood today are sadly too familiar and still too fresh in our memories," said U.S. Sen. John Cornyn.
No community should have to experience such violence once, let alone twice, he said.
"We're heartbroken something like this might have happened again," said President Obama, who was briefed by top defense and FBI leaders by phone while traveling on Air Force One.
Fort Hood has been resilient before, Gov. Rick Perry said. And it will again.
CNN's Joshua Rubin reported from Killeen, Texas; Ben Brumfield and Dana Ford reported and wrote from Atlanta. CNN's Steve Almasy, Nicole Dow, Greg Botelho, Evan Perez, Shimon Prokupecz, Pamela Brown, Brian Todd, Matt Smith, Barbara Starr, Carma Hassan and Devon Sayers contributed to this report.
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Read President Obama Statement:
President Barack Obama spoke Wednesday evening about a shooting at Fort Hood, Texas. The White House released a transcript of his remarks:
"Hello, everybody. I just got off the phone with Vice Chairman of the Joint Chiefs of Staff Sandy Winnefeld to get the latest report on the situation in Fort Hood. Obviously we're following it closely. The situation is fluid right now. But my national security team is in close contact with not just the Defense Department but the FBI. They are working with folks on the ground to determine exactly what happened to make sure that everybody is secure. And I want to just assure all of us that we're going to get to the bottom of exactly what happened.
Any shooting is troubling. Obviously this reopens the pain of what happened at Fort Hood five years ago. We know these families. We know their incredible service to our country and the sacrifices that they make. Obviously our thoughts and prayers were -- are with the entire community. And we are going to do everything we can to make sure that the community at Fort Hood has what it needs to deal with the current situation, but also any potential aftermath.
We're heartbroken that something like this might have happened again. And I don't want to comment on the facts until I know exactly what has happened, but for now, I would just hope that everybody across the country is keeping the families and the community at Fort Hood in our thoughts and in our prayers. The folks there have sacrificed so much on behalf of our freedom. Many of the people there have been on multiple tours in Iraq and Afghanistan. They served with valor; they served with distinction. And when they're at their home base they feel safe. We don't yet know what happened tonight, but obviously that sense of safety has been broken once again. And we're going to have to find out exactly what happened.
The Pentagon will undoubtedly have further briefings for you as we get more details about what happened.