FORT HOOD - US investigators believe the gunman who killed 13 people at Fort Hood, Texas, acted alone as they tried to to uncover the motive for one of the worst mass shootings ever on a US military base, officials said.President Barack Obama will Tuesday attend a memorial service here to honor victims of the shooting rampage attributed to Muslim US army doctor, Major Nidal Malik Hasan, who is also suspected of wounding 30 people.
"All evidence at this point indicates the suspect allegedly acted alone," Chris Grey, spokesman for the US Army criminal investigation division (CID), told reporters Saturday, adding that no motive had yet been established.
Criminal investigators were poring over evidence to determine if the alleged shooter -- who survived gun wounds and is under guard at a military hospital in San Antonio, Texas -- was motivated by Islamist ideology or had snapped under the pressure of his job counseling soldiers traumatized by combat.
Late Friday, there were signs that Hasan's condition was improving. Colonel John Rossi, deputy commander of Fort Hood, told reporters that while the suspect was still in an intensive care unit, "he is no longer on ventilator."
There was no word, however, whether he was able to answer investigators' questions.
Seventeen victims of Thursday's shooting remained hospitalized late Saturday, Rossi said.
A US-born Muslim of Palestinian heritage, Hasan 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.
Witnesses reportedly heard Hasan, who investigators believe fired more than 100 rounds during the incident, shout "Allahu Akbar!" (God is greatest) before unloading a semi-automatic weapon and a handgun at a troop processing center.
An initial search of Hasan'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 was Major Hasan, but the details fueled concerns that authorities may have missed warning signs prior to the attack at Fort Hood, Texas.
Neighbors 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 neighbor, Patricia Villa, according to The New York Times, handing over bags of vegetables, a mattress and clothing.
US officials and media reports highlighted Saturday the heroism of civilian police officer Kimberley Munley, 34, who selflessly rushed to the scene of the shooting and gunned down the assailant, despite being wounded herself.
According to Rossi, Munley underwent her second surgery early Saturday and was now listed in good condition"
"Kimberley Munley and family would like to extend their thanks and appreciation for all the thoughts and concerns surrounding from all around the nation," said a statement from the police officer's family read by Rossi.
Poignant details released here Saturday 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, and 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.
Specialist Ryan Hill, 28, came to the base with his young daughter Emma to put flowers and candles at the main gates as a mark of respect to the victims.
"It makes me mad. I don't how somebody can commit an act like that," Hill told AFP. "Those soldiers were ready to take off and deploy and they won't even get to do that."
In his weekly radio address earlier Saturday hailed the response of soldiers and civilians at the scene who rushed to help victims, tearing off bullet-riddled clothes to treat the injured and using blouses as tourniquets.
Troops based in Fort Hood, by area the world's largest US military base, have suffered the highest number of casualties and have undertaken multiple tours of duty in Iraq and Afghanistan.
The shooting has meanwhile 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.