| KILLEEN, Texas
KILLEEN, Texas Investigators searched for the motive on Friday behind a mass shooting at a sprawling U.S. Army base in Texas, in which an Army psychiatrist trained to treat war wounded is suspected of killing 13 people.
The suspected gunman, Major Nidal Malik Hasan, a Muslim born in the United States of immigrant parents, was shot four times by police, a base spokesman said. He was unconscious but in stable condition.
A woman died overnight from her wounds, raising the toll from Thursday's shootings to 13 dead and 30 wounded, said Colonel John Rossi, a spokesman at Fort Hood, the biggest military facility in the world.
Hasan was on a ventilator in a civilian hospital, Rossi said.
The Army refused to discuss possible motives while the investigation was under way. "We have to understand what caused the suspect to act in the way that he did," Army Secretary John McHugh said after observing a moment of silence at the base.
"This was a kick in the gut," said Army Chief of Staff George Casey.
The gunman, with two guns including a semi-automatic weapon, opened fire apparently without warning at the crowded Soldiers Readiness Processing Center, where troops were getting medical checkups before leaving for foreign deployments.
Hasan, 39, had spent years counseling severely wounded soldiers at the Walter Reed Army Medical Center in Washington, many of whom had lost limbs fighting in Iraq and Afghanistan.
He was transferred to Fort Hood in April and was to have been deployed to Afghanistan, where the U.S. military is engaged in an increasingly bloody war against Taliban and al Qaeda fighters.
The Army Criminal Investigation Command and the FBI are investigating the shootings and no charges have been brought against Hasan, McHugh said.
In Washington, President Barack Obama warned met with FBI officials, including agency director Robert Mueller, to discuss the incident.
"We don't know all the answers yet and I would caution against jumping to conclusions until we have all the facts," Obama said.
Hasan's cousin, Nader Hasan, said in interviews that he had agitated not to be sent overseas. "We've known over the last five years that was probably his worst nightmare," he said.
Nader Hasan also said his cousin had complained, as a Muslim, of harassment by fellow soldiers.
Hasan yelled "Allah akbar" -- Arabic for "God is great" -- just before the shooting, Chuck Medley, Fort Hood's director of Emergency Services, told Reuters.
But the Fort Hood commander, Lieutenant-General Robert Cone, said there was no evidence this was a terrorist attack.
American Muslim groups expressed regret and stressed that the incident appeared to have been carried out by a single disturbed individual.
"Thousands of Arab Americans and American Muslims serve honorably every day in all four branches of the U.S. military and in the National Guard," the Arab American Institute said.
Rossi said Thursday's shooting lasted 10 minutes. He said a female civilian police officer was the first to wound the gunman, who was wearing military garb.
Sergeant Andrew Hagerman, a military police officer, said Hasan was unconscious when he arrived.
"You're always surprised at how much carnage there is," said Hagerman, who returned in July 2008 from a tour of duty in Iraq. Soldiers ripped apart their uniforms to make bandages to care for the wounded, Hagerman said.
The United States has been engaged in six years of fighting in Iraq and nearly eight years of war in Afghanistan, which has put extra stress on the military and on individual soldiers.
In May, a U.S. soldier at a base in Baghdad shot and killed five fellow soldiers.
Multiple shooting incidents are not uncommon in the United States, where there are relatively lax gun controls.
Fort Hood personnel have accounted for more suicides than any other Army post since the U.S. invasion of Iraq in 2003, with 75 tallied through July of this year.
Fort Hood, about 60 miles from the state capital Austin, is home to about 50,000 troops.
(Writing by Chris Baltimore, editing by David Storey and Doina Chiacu)