FORT HOOD, Texas – From the first frantic 911 call that a shooter was rampaging through the Soldier Readiness Center on this sprawling Army base, it took police officer Kimberly Munley just four minutes to get there.

But it was already bloody chaos.

Munley heard shots and saw a rush of scared people, some wounded by gunfire, scrambling to get away.

Figuring that the shooter must be between buildings for medical and psychiatric services, she rounded the corner and saw him chasing after an already-wounded soldier. She fired twice.

"He turned to her and charged, firing rapidly. She returned fire and fell to the ground to help protect herself," said Chuck Medley, director of Fort Hood's emergency services.

Munley and the gunman hit each other simultaneously; she took shots in both legs and the wrist. Altogether, she fired four shots into his torso with her Beretta 9mm, dropping him to the ground and ending the worst mass shooting a U.S. military base has ever seen.

"She eliminated the threat. She did what she was trained to do," Medley said. "She, in my mind, saved countless lives."

Later, a military official said a second civilian officer, Mark Todd, also engaged the gunman.

Medley, who talked with Munley early Friday as she recovered, rightly identified the civilian officer as a hero.

But she wasn't the only one.

Many stayed to help the wounded at a scene most would have fled, falling back on their military and medical training. They worked furiously to save lives after Maj. Nidal Malik Hasan fired more than 100 rounds into a room where hundreds of unarmed soldiers were lined up for vaccines and eye tests. He had created a battle scene worse than most had witnessed in Iraq, killing 13 and wounding 30.

"There were many cases of soldiers and police officers yesterday putting their life on the line to save somebody else," Medley said, fighting back tears. "And that's what I saw."

Sgt. Andrew Hagerman, a military police officer from Lewisville who was on his rounds in the barracks area, was about a mile and a half away when the first crackle across the radio of "shots fired" came in.

He didn't think much of it – probably someone throwing firecrackers off the roof again.

But "shock and awe" came, he said, when he heard "Officer down." With sirens blaring, he made it to the scene in three minutes.

Even so, a tremendous amount of damage had been done in a short amount of time.

People were screaming. Some were on the ground, with soldiers hovering over them and ripping off their own shirts to stanch the bleeding. Some were being carried out of the two buildings where most of the carnage had occurred.

"I did spin a circle a couple of times, thinking, 'What do I need to do here?' " Hagerman said.

He walked past the gunman, unconscious on the ground in military fatigues. Ambulance drivers and medics had arrived, and, with his training taking over, Hagerman began directing traffic and sorting out the most seriously wounded who would need an ambulance first.

"It was controlled chaos," Hagerman said.

Even still, it was clear who the gunman was. Soldiers generally don't carry weapons on post, and Hasan "had a lot of weapons and magazines on him," Medley said.

Pfc. Marquest Smith of Fort Worth was in the medical services building because he's allergic to bee stings. Preparing to deploy to Afghanistan in January, he was filling out the paperwork to get the right medical tags.

He was just chatting with the ladies in the office. "Then, all we heard was popping noise. I thought, 'What is this?' " he said.

Soon, the screaming started.

He said his first reaction was to be still until the shooting stopped and he could escape. He instinctively went to the ground, but for a second, his foot caught up in the chair.

"Just then, a round came through the fabricated wall," he said, pointing to where the bullet had lodged in the heel of his tan boot. "Another second, and it would have been my spine."

There was a pause, but then the "popcorn popping" sound of gunfire returned.

"He wasn't running out of rounds, and so I thought, 'We better get out of here,' " Smith said.

He encouraged the two women to get up with him and followed them out the door.

He was safely out, but then he heard some cries of help and people yelling that they didn't want to die. He turned and went back in.

"I didn't know where he was," Smith said of the shooter. He grabbed two wounded soldiers lying near the door and dragged them outside by their collars.

"I don't know who they were. They just said, 'Help me. Get me out of here.' "

Col. Steve Beckwith, a doctor and triage expert, was tending a patient at the post hospital when a nurse told him there were gunshot injuries needing attention.

He started dispatching ambulances, then heard from his first driver that shots were still being fired. Suddenly, he was concerned that he had sent medics into harm's way.

Beckwith made his way to the ambulance bay, and already cars were pulling up – soldiers were rushing to the battle scene, picking up the wounded and taking them to the hospital before ambulances could even arrive.

"The first eight came in their own vehicles," he said.

Soon the ambulances started in a stream that would continue for an hour. He counted about 35 casualties banging through the ER doors.

"There were all sorts of makeshift bandages out there. A lot of them got care before they got to the hospital," he said.

Most were chest, trunk and extremity shots, which he dispatched. One had to be pronounced dead just as the victim was pulled out of the ambulance. Busily checking vital signs and issuing orders, Beckwith said he thought: "Good, we can save most of these folks," he said.

The wounded tried to help him prioritize. "People would be saying, 'Hey, I just got a leg; go get that guy,' " Beckwith said.

For ER nurse Janet DiPalma, the word came when a fellow nurse stuck her head into the office, announcing that there were multiple gunshot wounds coming in.

As she headed for the doors, she heard staffers on the phones with nurses and other medical personnel, some who didn't work at the hospital, who were calling and asking if they could come in and help.

"It was very intense," DiPalma said. "Soldiers were carrying soldiers. One was coming in right after the other. Your adrenalin kicks in."

It began right after 1:30, and the blood-soaked train continued. After about an hour, DiPalma said, she looked up and thought: "How many more?"

Col. Kimberly Kesling, chief of medical services, was at the hospital going into a meeting when an aide gave her and other top commanders the word of an ER on full alert. She thought initially it would be a relatively minor thing, a single patient or maybe two.

By the time she got to the ER, "it quickly became evident that it was a massive event," Kesling said.

In short order, Kesling said, all six operating rooms were filled with teams working on the injured.

Within an hour and a half, some had been airlifted to other hospitals, some were being treated, some in surgery.

Kesling said she was proud of her staff. Going from station to station, "I didn't see a cracked emotion," she said. "Today, tomorrow, that might be a different thing."

A surgeon, she had served in Iraq for nine months, returning in January 2004. For Kesling, the comparison was too real.

"I'd hoped to never see anything like that again."

"I'll tell you candidly, this was a kick in the gut, not only for the Fort Hood community, but also for the entire Army."

–Gen. George Casey, Army chief of staff

THE TOLL

The death toll from Thursday's mass shooting at Fort Hood rose to 13 on Friday. Twelve were soldiers. Twenty-eight injured remained hospitalized; two were released. Twelve are in ICU.

THE SUSPECT

Authorities say Maj. Nidal Malik Hasan, a 39-year-old Army psychiatrist, was wearing his uniform when he opened fire on about 300 unarmed soldiers lined up for vaccines and eye tests.

THE GUNBATTLE

Hasan fired more than 100 rounds. He was shot four times and brought down by Sgt. Kimberly Munley, 35, a civilian police officer. She was shot in the legs and the wrist but is expected to make a full recovery.

THE CONFUSION

"He was shot four times. His vital signs were gone, which is why they thought he was dead, and they resuscitated him. He's in stable condition but not in a condition to talk," said U.S. Rep. Michael McCaul of Austin, a senior Republican on the Homeland Security Committee.

THE WEAPONS

Hasan allegedly used a legally purchased 5.7 mm semiautomatic pistol known as a "cop killer" because some ammunition for it, legally available only to law enforcement and the military, can pierce bulletproof vests. It is not clear what ammunition was used. Records indicate Hasan recently bought the gun at Guns Galore in Killeen.

HASAN'S CONDITION

Hasan was taken Friday to the Brooke Army Medical Center at Fort Sam Houston, where he was listed in stable condition.

THE INVESTIGATION

The federal Joint Terrorism Task Force was assigned to the case, indicating a push to determine if Hasan acted alone and, even if he did, how he became radicalized.

"The picture we're getting is a guy who's internally conflicted, who's becoming increasingly more radicalized. The ultimate question is, is it a self-radicalization process or is he being influenced by outside factors," McCaul said.

Investigators examined Hasan's home, computer and garbage. Authorities are investigating whether he wrote Internet postings about suicide bombings and other threats.

MOTIVE UNCLEAR

Hasan cleaned out his apartment and left a phone message saying goodbye to a friend before the rampage. Relatives said he felt harassed because of his Muslim faith but did not embrace extremism. He was reportedly upset about being deployed to Afghanistan. In August, a soldier was charged after scratching Hasan's car. An apartment manager said the soldier served in Iraq and ripped off a bumper sticker that said: "Allah is Love."

LESSONS

Casey has asked Army leaders to review force protection measures. U.S. Rep. Mac Thornberry, R-Amarillo, said the House Armed Services Committee would probably look at how the Army responded to reports that Hasan's religious devotion conflicted with his ability to serve the military.

REMEMBRANCES

President Barack Obama ordered flags at the White House and other federal buildings be at half-staff until sunset Tuesday. The Army declared a day of mourning at Fort Hood. Exactly 24 hours after the shooting began, military bases around the world observed four minutes of silence. A candlelight prayer vigil was held at the fort.

A SOMBER GOODBYE

Texas Sens. Kay Bailey Hutchison and John Cornyn watched Friday as the 13 victims in flag-draped coffins were placed upon a C-17 and airlifted to Dover, Del., for forensic tests.