A US Army spokesman says the man authorities say went on a shooting spree at Fort Hood has been taken off a ventilator but still remains in intensive care at a military hospital.
Spokesman Colonel John Rossi told reporters on Saturday at Fort Hood that he is not sure if Major Nidal Malik Hasan is able to communicate.
Hasan was shot during an exchange of gunfire in Thursday's attack.
The military moved him on Friday to Brooke Medical Center in San Antonio, about 240km southwest of Fort Hood.
Army officials have said Hasan is "not able to converse".
Thirteen people were killed and 29 others wounded in Thursday's attack at Fort Hood.
Investigators on Saturday worked to uncover the motives behind the killing of 13 people and wounding of 30 others.
An initial search of the suspect's computer revealed no direct exchanges with known extremists, but US Army and FBI officials had yet to rule out possible links to terrorist groups, US media reported.
Earlier this year, the Federal Bureau of Investigation learned of internet postings by a man calling himself Nidal Hasan that expressed support for suicide bombings.
Investigators were not able to determine yet whether the writer and Major Hasan were the same person, but the details fuelled concerns that authorities may have missed warning signs prior to the attack at Fort Hood, Texas.
Neighbours reportedly said Hasan, 39, was in a rush when he gave away his belongings - including a Koran - shortly before Thursday's bloody shooting spree.
"I'm not going to need them," he told one neighbour, Patricia Villa, according to The New York Times, handing over bags of vegetables, a mattress and clothing.
A US-born Muslim of Palestinian heritage, Hasan, 39, had voiced dismay over US wars in Islamic countries and was distraught that he was about to be deployed to Afghanistan.
He reportedly said the US struggle against terror threats was a "war on Muslims," while his family alleged he was the target of prejudice and harassment over his Islamic faith.
Criminal investigators were poring over evidence to determine if the alleged shooter - who was under guard at a hospital - was motivated by Islamist political ideology or had snapped under the pressure of his job counselling soldiers traumatised by combat.
In Texas, poignant details of each of those killed in the rampage drove home the scale of the tragedy.
The victims included a 21-year-old mother-to-be Private Francheska Velez, who was due to return home to Chicago for maternity leave after a tour in Iraq; 56-year-old John Gaffaney, a psychiatric nurse who had just persuaded the military to let him return to active duty for deployment in Iraq; Private First Class Kham Xiong, 23, a father of three whose own father had fought communist forces in Laos during the Vietnam war.
President Barack Obama led the nation in mourning on Saturday, and sought to reassure a stunned military.
"Thursday's shooting was one of the most devastating ever committed on an American military base," he said. "And yet, even as we saw the worst of human nature on full display, we also saw the best of America."
The president hailed the soldiers and civilians who rushed to help victims, tearing off bullet-riddled clothes to treat the injured and using blouses as tourniquets.
Obama ordered flags to fly at half-staff at the White House and federal buildings, as troops at home and abroad held a minute's silence to mourn the dead.
The bodies of those killed were taken to the same mortuary at Dover Air Base in Delaware that handles fallen soldiers from the wars in Afghanistan and Iraq.
Hasan was moved meanwhile from a civilian to a military hospital, in part for security reasons, Fort Hood deputy commander Colonel John Rossi told reporters.
Hasan was shot and seriously wounded by a female civilian police officer who was being hailed as a heroine for ending his deadly rampage.
Witnesses reportedly heard Hasan shout "Allahu Akbar!" (God is great) as he opened fire in a troop processing centre with a semi-automatic weapon and a handgun.
Rossi said investigators believe Hasan fired more than 100 rounds during the incident.
US Army chief of staff General George Casey said the attack was "a kick in the gut, not only for the Fort Hood community but for the entire army."
Fort Hood, by area the world's largest US military base, has borne the brunt of the wars in Iraq and Afghanistan. Troops based here have suffered the highest number of casualties and have undertaken multiple tours of duty.
The shooting also raised delicate questions about Muslim soldiers serving in the military, as some commentators warned of an Islamic "fifth column" infiltrating the army while Islamic groups called for calm amid concerns of a backlash.
Casey said after a visit to the base that he too feared a backlash.
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