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The U.S. flag flies at half-mast in front of the army's III Corps headquarters at Fort Hood, Texas, on Friday. ((LM Otero/Associated Press))

The gunman who killed 13 people and injured 30 in a shooting rampage at a Texas military base on Thursday fired off more than 100 rounds of ammunition, an army spokesman said.

Col. John Rossi, deputy commanding general at Fort Hood, said that number was based on shell casings found and the number of victims who were shot. Rossi said 46 people sustained gunshot wounds, including those who were killed.

Twenty-three people remain in hospital.

Rossi also said two civilian police officers exchanged gunfire with the gunman and brought him down. The suspected shooter, Maj. Nidal Malik Hasan Hassan, was shot four times. He is in a coma and listed in stable condition.

Meanwhile, U.S. federal authorities searched the apartment in Killeen, Texas, of Hasan and seized his computer, looking for clues as to what may have caused the violent attack.

The family of the 39-year-old army psychiatrist issued a statement Friday, calling the actions of their cousin "despicable and deplorable." Kim Fuller, a spokeswoman for his family, said relatives in Northern Virginia are reaching out to law enforcement Friday to offer insight.

Balked at going to Iraq

Hasan was slated to be deployed to Iraq but didn't want to go, according to a military official who spoke on condition of anonymity.

Authorities have been unable to interview Hasan because he's in a coma and breathing with the help of a ventilator. Despite being shot four times, he is expected to live. He was transferred Friday to Brooke Army Medical Center in San Antonio, Texas, where a spokesperson said he was in stable condition.

Military officials had originally reported Hasan dead, but Rossi confirmed Friday that in earlier reports authorities had mistaken one of the victims as the shooter.

The incident began when a soldier, armed with two handguns, stood on a table and opened fire at about 1:30 p.m. local time in the base's Soldier Readiness Center, where troops go through medical screening before being deployed overseas or after returning from a posting.

Lt.-Gen. Robert Cone told NBC's Today show that the shooter shouted "Allahu Akbar!" — Arabic for "God is great" — before he began firing.

A law enforcement official, who spoke on condition of anonymity, said the shooter used a 5.7-mm pistol, bought legally at a local gun store. An army official said the attacker also carried a second handgun, but a law enforcement official said there was no indication it had been fired.

Neighbours said Hasan had given away food and possessions in previous days and told his landlord he was moving out this week.

Next-door neighbours Jacqueline Harris, 44, and her boyfriend, Willie Bell, said Hasan called Thursday at 5 a.m. and left a goodbye message. Bell said Hasan bid farewell, saying, "Nice knowing you, old friend. I'm going to miss you."

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Maj. Malik Nadal Hasan is reported to be the gunman who opened fire in Fort Hood, Texas, killing 13 people. ((U.S. Department of Defence/Reuters))

Officials on Friday said the death toll had risen after another victim died overnight in hospital. Rossi said 12 soldiers and one civilian were among those who died in the shooting, but did not release any names as not all families had been notified.

Rossi would not speculate on a motive behind the attack, saying that was a subject for investigators to handle.

"At this point we have one suspect — as we said, a lone shooter," said Rossi.

Suspect counselled soldiers

A cousin, Nader Hasan, told the New York Times that Hasan counselled soldiers returning from Iraq and Afghanistan with post-traumatic stress disorder, so he knew the effects of war first-hand.

"He was mortified by the idea of having to deploy," Nader Hasan said. "He had people telling him on a daily basis the horrors they saw over there."

Col. Steven Braverman said he was not aware of any problems with the job performance of Hasan, who worked as a psychiatrist at the hospital counselling soldiers, but would not comment on any problems outside of work.

Retired colonel Terry Lee, who said he had worked with Hasan, told Fox News that Hasan had hoped U.S. President Barack Obama would pull troops out of Afghanistan and Iraq and got into frequent arguments with others in the military who supported the wars.

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Col. John Rossi, right, looks on as Col. Steven Braverman speaks during a briefing to media outside Fort Hood. ((LM Otero/Associated Press))

Internet postings investigated

U.S. military officials said Hasan had come to their attention at least six months before the attack because of internet postings that appeared to come from him that discussed suicide bombings and other threats. Officials are still working to confirm Hasan's connection to the postings, but an official investigation was never opened.

One of the postings that authorities reviewed is a blog that equates suicide bombers with a soldier throwing himself on a grenade to save the lives of his comrades.

"He is a brave hero that sacrificed his life for a more noble cause," the posting says.

Faizul Khan, a former imam at a mosque Hasan attended in Silver Spring, Md., said he spoke often with Hasan about how Hasan wanted to find a wife. Hasan was a lifelong Muslim and attended prayers regularly, often in his army uniform, Khan said.

In an interview with the Washington Post, Hasan's aunt, Noel Hasan of Falls Church, Va., said he had been harassed about being a Muslim in the years after the Sept. 11, 2001, attacks and he wanted out of the army.

"Some people can take it and some people cannot," she said. "He had listened to all of that and he wanted out of the military."

Obama called the Texas shooting "a horrific outburst of violence" and pledged support for the Fort Hood community.

Flags to be held at half-mast

Obama said Friday that flags at the White House and all federal buildings will be held at half-mast until Veterans Day as a tribute to those killed during the attack at Fort Hood.

"We don't know all the answers yet, and I would caution against jumping to conclusions until we have all the facts," Obama said in a brief statement from the White House.

"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 yesterday in one of the worst mass shootings ever to take place on an American military base," he said.

Gen. George Casey, the U.S army chief of staff, called the attack a "kick in the gut."

"We take care of our own. We grieve as a family," Casey told reporters at a Fort Hood press conference.

With files from The Associated Press