The military psychiatrist responsible for a shooting spree that left 13 dead remained in a coma today, frustrating attempts to work out what made him kill.
Major Nidal Malik Hasan was last night said to be in a critical but stable condition as many of his victims continued to fight for their lives in hospital.
Meanwhile investigators resumed their search for a motive to the crime.
Witnesses are said to have heard the suspect cry "Allahu Akbar" - Arabic for "God is great" - before opening fire at the sprawling military complex in Texas.
Alleged links to extremist websites were being examined as authorities attempted to work out if Hasan's rampage was driven by mental breakdown or ideological rage.
Hasan, a devout American-born Muslim, was shot several times in the aftermath of the rampage by a civilian police officer who was yesterday hailed as a hero.
Lieutenant General Bob Cone said Sgt Kimberly Munley and her partner responded to reported gunfire within three minutes.
She then disabled the suspect despite being shot herself in the process.
"It was an amazing and an aggressive performance by this police officer," the military spokesman said.
Shortly before her arrival, Hasan - armed with two non-military issue pistols, including a semi-automatic - entered a section used to prepare soldiers for deployment overseas and started firing.
Within minutes, 12 soldiers and a civilian at the base were dead or dying in the worst mass shooting yet at a military base in the US.
At least 30 others were injured in an attack described by President Barack Obama as a "horrific outburst of violence".
The shootings began on Thursday at around 1.30pm local time (7.30pm GMT) at Fort Hood's readiness centre.
The compound - the US's largest military base - yesterday observed a day of mourning.
Mr Obama ordered federal buildings to fly the US flag at half-mast until Veterans' Day (November 11) as a "modest tribute" to the dead at Fort Hood.
In brief remarks delivered in the White House Rose Garden, the president said he had met FBI chiefs to be updated on the investigation.
He added: "We don't know all the answers yet, and I would caution against jumping to conclusions until we have all the facts.
"What we do know is that there are families, friends and an entire nation grieving right now for the valiant men and women who came under attack in one of the worst mass shootings to take place on an American military base."
Hasan, 39, from Virginia, was due to be sent to Afghanistan, something family members said would have been his "worst nightmare".
Defence sources said at least six months ago Hasan came to the attention of law enforcement officials because of internet postings about suicide bombings and other threats.
They included posts which compared suicide bombers with soldiers who threw themselves on a grenade to save the lives of their comrades.
Investigators were not certain whether Hasan had written the posts and a formal investigation had not been opened before the shooting, said the sources.
Yesterday they examined his computer, his home and his rubbish in an attempt to learn what led to his outburst of violence.
Many of the questions are likely to go unanswered unless and until Hasan emerges from his coma.