The soldier suspected of shooting dead three people before killing himself at the Fort Hood Army base in Texas was under psychiatric care but showed no signs of violence or suicidal tendencies, a US official said on Thursday.
No motive was given for the rampage, which also left 16 wounded, in what was the second mass shooting in five years at one of the largest military bases in the United States, raising questions about security at such installations. Officials have so far ruled out terrorism.
The gunman, who had been treated for depression and anxiety, was yet to be officially named but security officials said preliminary information identified him as 34-year-old Ivan Lopez.
He is suspected of smuggling a recently purchased Smith & Wesson .45 caliber pistol on to the base, which was used in the shootings.
US Army Secretary John McHugh said the soldier, who joined the service in 2008, had served two tours of duty abroad, including four months in Iraq in 2011. He had no direct involvement in combat and had not been wounded.
"He was undergoing a variety of treatment and diagnoses for mental health conditions, ranging from depression to anxiety to some sleep disturbance. He was prescribed a number of drugs to address those, including Ambien," McHugh told a US Senate committee hearing.
McHugh said the soldier and his wife were from Puerto Rico and that he had served in the Puerto Rican national guard before joining the US Army.
Puerto Rico National Guard Major Jamie Davis told Reuters that Lopez was the same person believed to be at the center of the Fort Hood shooting.
Lopez served in the Puerto Rico National Guard from January, 1999 to 2009, in an infantry unit and as a band member, both military combat training assignments; he also had a six-month stint as part of an observation mission in the Sinai, Egypt, in 2006, Davis said.
At the modest blue-and-gray apartment building in Killeen where Ivan Lopez lived with his wife and 2-year-old daughter, American flags flew and "Welcome home" signs adorned the walls of a place favored by soldiers rotating through the base.
Army chaplains visited the family on Thursday.
Shaneice Banks, 21, a self-described Army wife, was with Lopez's wife when news of the shooting broke.
"She heard her husband's name on the news and she just lost it," Banks told Reuters.
Another neighbor, Mahogoney Jones, 21, said the wife was in a state of panic. "She's calling and calling her husband because she feels something is wrong. She kept screaming 'No answer! No answer!'".
Jones said she last saw Lopez when he came home for lunch on the day of the shooting.
"He was calm. He petted my dog and then went back to base," she said.
Military families at Fort Hood, a base still reeling from the 2009 attack when an Army psychiatrist killed 13 people and wounded 32 others, appeared shaken on Thursday.
There are about 45,000 soldiers and airmen assigned to the 335-square-mile (870-square-km) base along with nearly 10,000 civilian employees, according to Fort Hood.
Doctors at one local hospital said three shooting victims remained in critical condition.
The shooter, who arrived at Fort Hood in February, had "self-reported" a traumatic brain injury after returning from Iraq but was never wounded in action, said Fort Hood commanding officer Lieutenant General Mark Milley.
Before the shooting, he was being evaluated for PTSD, or post traumatic stress disorder.
It was not clear what spurred the gunman to enter two base buildings and open fire on fellow soldiers at about 4:00 p.m. local time (2100 GMT) on Wednesday.
The shooter walked into one of the unit buildings, opened fire, then got into a vehicle and fired from there. He then went into another building and opened fire again, until he was engaged by Fort Hood law enforcement officers, Milley said.
When confronted by a female military police officer in a parking lot, he shot himself with his semi-automatic weapon.
The incident is the third shooting at a military base in the United States in about six months that, along with a series of shootings in schools and malls, has sparked a national debate over gun violence.
US President Barack Obama was "heartbroken" that another shooting had occurred, and said the incident "reopens the pain of what happened at Fort Hood five years ago."
The latest violence highlights the US military's so-far frustrated efforts to secure its bases from potential shooters, who appear to target the facilities.
Fort Hood, a base from which soldiers prepare to deploy to Iraq and Afghanistan, had overhauled its security to better deal with potential "insider threats" after the 2009 rampage, when an Army psychiatrist killed 13 people and wounded 32 others.
Retired Army Sergeant Alonzo Lunsford, who was shot multiple times in the 2009 incident, said the military has not done enough to treat the mental scars of those who have served in combat regions.
"The military needs to go ahead and stop talking about the problem and talking about what we're going to do. Just do it," Lunsford said.