16 hurt, 4 dead including gunman

• 16 more people are injured at the Army installation


• Shooter Ivan Lopez kills himself after officer confronts him in parking lot


• Lopez had mental health issues, an official says


• President Obama: 'We're heartbroken something like this might have happened again'

Stay safe and share your images with iReport.

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.

Fort Hood confirms active shooter on base

Luci Hamlin and her husband, Spc. Timothy Hamlin, wait to get back to their home at Fort Hood after a shooting at the Texas Army post on Wednesday, April 2. Multiple people were killed and others injured when a shooter opened fire, a senior military official and law enforcement official told CNN. The officials said the suspected shooter was among the dead.

A police officer checks drivers' IDs outside the main gate at Fort Hood.

Krystina Cassidy and Dianna Simpson, waiting outside the Bernie Beck Gate at Fort Hood, try to contact their husbands, who are stationed at the post.

A Bell County Sheriff's Department official stands near a vehicle as cars are checked at the Bernie Beck Gate.

An ambulance makes its way to Fort Hood.

Military personnel and civilians wait outside Fort Hood for updates on the situation.

Vehicles wait at a closed entrance to Fort Hood.

A military police officer stops a car.

Traffic near the main gate of Fort Hood.

Lt. Savanah Hess, a nurse, waits in her car to enter the locked-down post.

Military police direct traffic outside Fort Hood.

Fort Hood shooting

US officials: Fort Hood shooter is dead

Soldier calls from Fort Hood shelter

Obama: We will get to the bottom of this

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.

Lt. General: Don't know shooter's motive

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.

Emotional torment

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.

Lockdown

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.

Not again

Reporters prodded Milley about the 2009 shooting and Lopez' rampage -- a repeat tragedy.

But 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.