The gunshots came out of the blue.
An Army psychiatrist, trained to treat soldiers under stress, allegedly opened fire Thursday in a crowded medical building at Fort Hood, Texas. When the assault ended minutes later, the attack had become what is believed to be the largest mass shooting ever to occur on a U.S. military base. Twelve were killed, 31 wounded.
Nidal Malik Hasan, a major who had made a career in the military, fired a pair of pistols, one of them semi-automatic, dropping and scattering people as they waited to see doctors, according to authorities. Hasan and a civilian policewoman exchanged fire, they said. Both were hit. Both survived.
When the gunfire stopped, soldiers schooled in battlefield medicine ripped their clothes to make tourniquets and bandages. Someone hustled to seal off an auditorium in the same building where 138 troops were marking their graduation from college. Sirens typically used to warn of tornados sweeping across the plains alerted residents, schools locked down and the Fort Hood community struggled to understand what had just happened.
In the aftermath, a string of unanswered questions remained about the suspect's motives, his background and whether the military was aware that he posed a risk to his colleagues.
In Iraq, an Army journalist telephoned his wife, who lives on the base. When she did not answer, he turned to e-mail. She said there had been shootings and an order to secure all doors and windows.
"This is ridiculous," Naveed Ali Shah, the soldier, told his wife. "I'm in the war zone, not you!"
The accused gunman, initially reported killed but later revealed to be in custody in a hospital, is a Virginia-born doctor who once practiced at Walter Reed Army Medical Center. The motive remains unclear, although some sources reported the suspect is opposed to U.S. involvement in Afghanistan and Iraq and upset about an imminent deployment.
The attack erupted shortly after lunchtime on the sprawling complex that has absorbed more than 500 fatalities in Iraq and Afghanistan, more than any other base. Investigators said their initial impression was that the gunman had acted alone.
The victims were taken to various hospitals, where local residents were lining up to donate blood.
"It's a terrible tragedy. It's stunning," Army Lt. Gen. Robert Cone told reporters gathered outside the facility northeast of Austin. "Soldiers and family members and many of the great civilians who work here are absolutely devastated."
Hasan, 39, graduated from Virginia Tech in 1997 and earned a doctorate in psychiatry from the Uniformed Services University of the Health Sciences in Bethesda, Md. He spent at least six years at Walter Reed before moving to Fort Hood.
He had been a "very devout" worshiper at the Muslim Community Center in Silver Spring, Md., attending prayers at least once a day, often in his Army fatigues, said Faizul Khan, a former imam there.
"To know something like this happened, I don't know what got into his mind," Khan said. "There was nothing extremist in his questions. He never showed any frustration."
President Barack Obama promised to "get answers to every single question about this horrible incident." He offered his prayers to the wounded and the families of those killed, calling them "men and women who have made the selfless and courageous decision to risk -- and at times give -- their lives to protect the rest of us."
"It's difficult enough when we lose these brave Americans in battles overseas," Obama said. "It is horrifying that they should come under fire at an Army base on American soil."
Thousands of soldiers have passed through the gates of Fort Hood on their way to Iraq and Afghanistan, and more than 500 have not come home. Post-combat stress has been an acknowledged problem on the base, and this year alone, 10 Fort Hood soldiers have committed suicide.
Lt. Gen. Rick Lynch, the former base commander, won praise for trying to reduce stress. Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, told the Army Times that "there's something going on at Hood that I think is extraordinary that we need to emulate until we find something better."