Houston: The US Army has said the gunman, who opened fire at Fort Hood military base, was mentally unstable and that was believed to be a "fundamental, underlying cause" of the shooting incident.
Speaking at a news conference, base commander Lt. Gen. Mark Milley said a verbal altercation with another person at the post "may have immediately preceded the shooting". He confirmed the gunman, who yesterday killed his three colleagues, was 34-year-old Ivan Lopez from Puerto Rico.
Milley said it was not confirmed whether Lopez targeted specific people. But, he said, "There is no indication at this time he was targeting specific individuals."
"At this point we have not yet ruled out anything whatsoever," he said, adding that there are no indications that Lopez had any links to terrorist organisations, either national or international.
Milley said Lopez purchased the gun - a .45 calibre Smith and Wesson semi-automatic pistol - on March 1 from Guns Galore, the same gun store in Killeen from where Major Nidal Hasan bought weapons he used in a mass shooting in 2009.
In 2011, an Army private from Kentucky, Naser Jason Abdo, had bought from the same store gun powder he used to make a shrapnel bomb with which he intended to kill soldiers in Killeen. Lopez had not registered a weapon, Milley said.
Extending condolences to the families of the victims, Milley said an investigation is ongoing. He said that of the 16 people injured, some remain hospitalised at Darnell Army Medical Center and at Scott and White Hospital ? Temple, which took in the most critically injured.
Four patients were discharged from Scott and White Hospital in Temple, while five others remain, said Beth Valvano, a hospital spokeswoman. Three who were in critical condition have been upgraded to serious, and two other patients are in good condition, she said.
A memorial ceremony is planned for next week, but Milley said a time and date would be announced later.
According to the Commanding General, two soldiers wounded in the attack were the first to call 911 at 4:16 p.M. Wednesday.
A female military police arrived and began searching the scene at 4:20 p.M. Milley would not identify the officer, but said she saw Lopez who approached her when he was about 20 feet away. He put his hands up, but then pulled a handgun, and she fired her weapon at him, Milley said.
Lopez then shot himself in the head, Milley said. The officer was not wounded, and Milley said he did not know if she had hit Lopez with any shots.
Milley said he saw various acts of "clear heroism," including the actions of the officer and of medical personnel at Darnall and Scott and White.
US Senator John Cornyn also expressed his condolences at the press conference. "What I see is a community that has come together in a time of crisis and heartbreak and is pulling together," Cornyn said.
"This community is no stranger to hardships and challenges, and they have risen and met the test every time. I`m certain they will do that again."
Cornyn said a thorough review would be done to see if there are "any gaps in current policies" that need to be addressed.
At this time, there is no change in the military policy that forbids weapons from being carried on military posts and bases, officials said.
Fort Hood has 100,000 people working and living there and any type of "pat-down search" is not possible, Milley said.
Cornyn called mental health issues "the most vexing," adding that many people involved in combat have no mental health issues.