Washington - US authorities were digging into the background of the Army psychiatrist suspected of carrying out the shooting at Fort Hood, Texas, to determine a motive for the attack that killed 13 people. The alleged gunman, Major Nidal Malik Hasan, remained in critical condition in the hospital on Friday but was expected to survive. One report said the 39-year-old devout Muslim was in a coma. There were 30 people wounded in Thursday's assault, authorities said.
Hasan shouted "Allahu Akbar" - God is great - before unleashing two handguns at the Army base's centre that prepares soldiers for deployment overseas, Lieutenant General Robert Cone, the base commander, told NBC News.
Meanwhile, President Barack Obama said he was receiving updates on the investigation and cautioned against drawing any conclusions about the shooter's motive. US officials have not ruled out the possibility of terrorism although it was appearing unlikely.
"We don't know all of the answers yet, and I would caution against jumping to conclusions until we have all of the facts," Obama said.
Obama ordered the US flags of all federal government buildings to be flown at half-staff to mourn the victims - 12 soldiers and one civilian police officer. The Pentagon planned a moment of silence at military installations around the world to take place at 2:34 EST (1934 GMT).
"This is a modest tribute to those who lost their lives even as many were preparing to risk their lives for their country," Obama said.
Secretary of the Army John M McHugh and General George Casey, the Army chief of staff, travelled to Fort Hood Friday morning and will hold an afternoon press conference, Colonel Catherine Abbott, an Army spokeswoman, said.
Meanwhile, details were emerging about Hasan, as acquaintances expressed shock that he could have been behind the crime but also that he had grown disgruntled by his pending deployment to Iraq.
US media reported that Hasan had sought to be discharged from the Army, and relatives said he was horrified about the possibility of going to Iraq and had grown tired of being harassed by other soldiers because of his faith.
As an Army psychiatrist, Hasan had treated soldiers returning from the war in Afghanistan and Iraq for post-traumatic stress disorder and other ailments.
His cousin, Nader Hasan, told the New York Times that the major was "mortified by the idea of having to deploy. He had people telling him on a daily basis the horrors they saw over there."
His aunt just outside Washington in Falls Church, Virginia, told the Washington Post that Hasan had been heckled by fellow soldiers for his Muslim faith in the years since the September 11, 2001, terrorist attacks on the United States.
"I know what that is like," Noel Hasan was quoted as saying. "Some people can take it, and some cannot. He had listened to all of that, and he wanted out of the military, and they would not let him leave even after he offered to repay" for his medical training.
Hasan has been treating soldiers at the Walter Reed Army Medical Centre in Washington beginning in 2003 before being sent to Fort Hood in advance of his deployment. He was facing his first deployment to a war zone since he joined the Army in 1995.
Hasan reportedly opposed the wars in Iraq and Afghanistan and was not shy about conveying his position to co-workers and friends.
Colonel Terry Lee, a colleague of Hasan's, told Fox News that Hasan had once said that Muslims should "stand up and fight against the aggressor" and that the United States should not be fighting the wars in Iraq and Afghanistan.
Hasan had been impacted by his work with injured solders, and by the physical and mental injuries he saw at Walter Reed, his aunt said.
"He must have snapped," Noel Hasan told the Post. "They ignored him. It was not hard to know when he was upset."
Asked about the mood at Walter Reed in light of the shooting, a spokesman would only say: "The whole Army is feeling this incident."
Born in Virginia, Hasan grew up in the Washington area and frequented the Muslim Community Center in Silver Spring, Maryland, which borders the nation's capital. He would wear Army fatigues, according to the former imam there, Faizul Khan.
Khan told the Washington Post that he came to the mosque several times looking for a suitable woman to marry, but had "too many conditions" to be satisfied with anyone. His aunt, Noel Hasan, described him loner without a girlfriend, according to the Post.
There had been initial reports after the rampage that there might might have been two other gunmen. Two soldiers were questioned and later released and the military concluded that Hasan allegedly acted alone, Cone said. A civilian police officer shot Hasan four times, ending the spree. She also suffered gunshot wounds.
The shootings shocked the military base accustomed to grieving for soldiers killed abroad. The rampage also brought the war closer to home and highlighted the growing stress on the men and women in who have been repeatedly deployed to Iraq and Afghanistan for extended combat duty during the last six to nine years.
The Washington-based Council on American-Islamic Relations (CAIR) condemned the killings as an unjustified "cowardly attack."
"No religious or political ideology could ever justify or excuse such wanton and indiscriminate violence," CAIR said. "The attack was particularly heinous in that it targeted the all-volunteer army that protects our nation."
