Pfc. Marquest Smith, who is heading to Afghanistan in January, was filling out medical paperwork about his bee-sting allergy when he heard a loud popping noise.
Moans followed, then the sudden, urgent shout of "Gun!"
Smith poked his head over the cubicle's partition and saw an extraordinary sight: An Army officer with two guns, firing into the crowded room.
The 21-year-old Fort Worth native quickly grabbed the civilian worker who'd been helping with his paperwork and forced her under the desk. He lay low for several minutes, waiting for the shooter to run out of ammunition and wishing he, too, had a gun.
After the shooter stopped to reload, Smith made a run for it. Pushing two other soldiers in front of him, he made it out of the Soldier Readiness Processing center — only to plunge into the building twice more to help the wounded.
Smith had survived the worst mass shooting on an American military base: a rampage of more than 100 shots that left 13 dead and more than two dozen wounded, including the alleged shooter, Army psychiatrist Maj. Nidal Malik Hasan.
The suspected gunman's Palestinian uncle told Fox News that the family was "shocked" by the allegations and had no indication Hasan was capable of such violence.
"He was very quiet, very nice, never been upset, always a smile," Rafiq Ismail told Fox News' Reena Ninan in an interview in Ramallah, the West Bank. "Til now, we did not believe he did it. It's not him. ... Something happened, made him snap or something."
Ismail said Hasan's parents died several years ago and he had been "coping" with the loss since. He said his nephew was against the Sept. 11 terrorist attacks, but was dismayed by the anti-Muslim backlash.
"He was saying they were killers, what they did in 9/11. He did not approve of it," Ismail said. "But I tell you he did not like the reaction ... collective punishment for the background Arabic or Islam."
The massacre could have been much worse, but for the heroics of Smith and others — like the 19-year-old private who ignored her own wounds, and the diminutive civilian police officer whose gunfire helped take down Hasan.
"Unfortunately over the past eight years, our Army has been no stranger to tragedy," said a somber Gen. George Casey, Army chief of staff. "But we are an Army that draws strength from adversity. And hearing the stories of courage and heroism that I heard today makes me proud to be the leader of this great Army."
Home of the 1st Cavalry and 1st Army Division West, Fort Hood has seen more than its share of deployments and casualties in the past eight years.
As a psychiatrist, Hasan, 39, had listened to soldiers' tales of horror. Now, the American-born Muslim was facing imminent deployment to Afghanistan. In recent days, Hasan had been saying goodbye to friends. He had given away many of his possessions, including copies of the Holy Koran.
At 2:37 a.m. Thursday and again around 5, Hasan called neighbor Willie Bell. Bell could normally hear Hasan's morning prayers through the thin apartment walls, but Hasan skipped the ritual Thursday.
Bell didn't pick up either time, but Hasan left a message.
"Nice knowing you, old friend," Hasan said. "I'm going to miss you."
About an hour later, surveillance cameras at a 7-Eleven across from the base captured images of a smiling Hasan, dressed in a long white garment and white kufi prayer cap, buying his usual breakfast — coffee and a hash brown.
At the processing center on the southern edge of the 100,000-acre base, soldiers returning from overseas mingled with colleagues filling out forms and undergoing medical tests in preparation for deployment.
Around 1:30 p.m., witnesses say a man later identified as Hasan jumped up on a desk and shouted the words "Allahu Akbar!" — Arabic for "God is great!" He was armed with two pistols, one a semiautomatic capable of firing up to 20 rounds without reloading.
Packed into cubicles with 5-foot-high dividers, the 300 unarmed soldiers were sitting ducks. Those who weren't hit by direct fire were struck by rounds ricocheting off the desks and tile floor.
When he decided that Hasan wasn't close to being out of ammo, Smith made a dash for the door. He'd made it outside when he heard cries from within.
"I don't want to die."
"This really hurts."
"Help me get out of here."
Smith rushed back inside and found two wounded. He grabbed them by their collars and dragged them outside.
His second time through the door, he ran into the shooter, whose back was to him. Smith turned and fled, bullets whizzing by his head and hitting the walls as he rushed outside.
Around this time, Fort Hood Police Sgt. Kimberly Munley got the call of "shots fired." The SRP isn't on Munley's beat; she was in the area because her vehicle was in the shop.
Munley, 34, was on the scene within three minutes.
Just over 5 feet tall, Munley is an advanced firearms instructor and civilian member of Fort Hood's special reaction team. She had trained on "active shooter" scenarios after the April 2007 mass shooting at Virginia Tech University. She didn't wait for backup.
As Munley approached the squat, rectangular building, a soldier emerged from a door with a gunman in pursuit. The officer fired, and the uniformed shooter wheeled and charged.
Another officer, Senior Sgt. Mark Todd, also responded to the sound of gunfire. He arrived to find Hasan "just standing there, hiding behind a telephone pole."
"He just looked like he was calm and he was just pointing, it was almost like he was pointing his finger at me," Todd told CNN in an interview late Friday. "But then I seen the weapon. ... I just know I seen the weapon and muzzle flashes and then that's when we returned the fire."
Munley was hit at least three times in the exchange — twice through the left leg and once in her right wrist. Hasan was hit four times. It's not clear whose bullets hit the suspect, but from the first shots to the last, authorities say the whole incident lasted less than 10 minutes.
Pfc. Jeffrey Pearsall, 21, from Houston, was waiting outside in the parking lot for Smith. He was talking to his brother on a cell phone when a group of soldiers ran out the door and a window shattered.
It was only then that he heard the gunshots.
He pulled his pickup truck forward, then hopped out and helped the wounded into the bed. He loaded as many as he could and sped off to the base hospital.
Next door, at the Howze Theater, Spc. Elliot Valdez was filming a graduation ceremony for soldiers who'd completed correspondence courses. Several proud scholars were posing for a group shot when Valdez heard a pounding at the side door.
The door burst open and the theater filled with shouts of "Medic!" and "Stay in the building!" A combat videographer who returned from a 15-month Iraq tour in January, some of it in the notorious Sadr City slums, Valdez ran out into the sunlight.
Crouching as he continued to roll tape, Valdez could see windows broken by fleeing victims. He saw a soldier in his Class A dress uniform with a gunshot in his back. Soldiers in flowing black graduation robes and purple sashes rushed to help.
Pfc. Amber Bahr, 19, of Random Lake, Wis., tore up her blouse and used it as a tourniquet on a wounded comrade. It was only later that she realized she'd been shot in the back, the bullet exiting her abdomen.
Sgt. Andrew Hagerman, a military police officer, was patrolling a housing area when word of shootings crackled over his radio.
As he arrived at the processing center, bloodied soldiers, some shirtless, were already treating each other on the grass outside, ripping pant legs off and tying off wounds. Munley — with whom Hagerman had exchanged small talk on patrols — was being loaded into an ambulance.
Hasan lay on the ground, his two handguns beside him, as medical personnel struggled to remove his handcuffs to treat his wounds.
Hagerman entered the building, took a deep breath and asked himself: "What do I need to do?"
He picked his way around the room's edges, careful not to step in pools of blood or to kick any spent shell casings. He had seen death during his two tours in Iraq, but nothing that compared with this.
In the confusion, Army Reserve Spc. Grant Moxon, 23, lost his cell phone. He borrowed a comrade's phone to send a text to his family in Lodi, Wis.
The message stated simply: "Grant. I was shot in the leg. I'll be OK."
Sgt. Howard Appleby, 31, was at the hospital for his regular meeting with a psychiatrist. Appleby, who was born in Jamaica and grew up in New York City, sustained a traumatic brain injury and has post-traumatic stress disorder from a roadside bomb blast during a tour in Iraq.
His appointment canceled, Appleby found himself pulling the dead and wounded from ambulances. In combat, he was used to one or two casualties a day. "This," he thought, "is crazy."
Lt. Col. Larry Masullo, an emergency room physician from Farmingdale, N.Y., was heading into a monthly meeting to review new doctors' credentials when he heard of the shootings.
"Yeah, OK," he said. "Multiple gunshot wounds. Is this a drill?"
In the next hour and a half, he would treat nearly two dozen soldiers.
For several hours, authorities feared there were several gunmen. By the end of the day, it was clear Hasan had acted alone, they said.
Hasan, hooked up to a ventilator, was moved Friday to a military hospital in San Antonio. The woman who stopped him, Munley, awaited surgery Friday to remove the bullets from her leg. Her husband was flying in from Fort Bragg, N.C.
Her boss, Chuck Medley, was thankful. "If an officer had to be close by to respond," he said, "Kim Munley is someone we'd want to be there."
Marquest Smith says some of the people he helped made it. But he knows others did not.
Afterward, Smith noticed a hole in heel of his right combat boot. A bullet had entered the boot, but he had somehow escaped injury — at least the physical kind.
After the adrenaline wore off, Smith was overwhelmed by a sense of betrayal, because this assailant who spilled so much blood was a soldier.
"We're supposed to be a family," he said.
Fox News' Reena Ninan and The Associated Press contributed to this report.