U.S. President George W. Bush addresses a convocation a day after killings at Virginia Tech in Blacksburg, Virginia, April 17, 2007. [Reuters]

On a university campus of 2,600 acres, with more than 26,000 students, ironclad security is not a practical goal. Even so, tough questions swiftly surfaced as to how effectively Virginia Tech authorities responded to Monday's horrific massacre that left 33 people, including the shooter, dead.

Why were campus police so sure the threat was contained in one dormitory, when most of the killings occurred two hours later in a classroom building?

Why did they think the assailant might have left the campus after those initial shootings that killed two?

Why was there a lag of more than two hours after the first shootings before an alarm was e-mailed campuswide - around the time another, more deadly burst of carnage occurred? And more generally, some security experts wondered, was the school's crisis planning and emergency communications system up to the task?

Something went wrong?

Clearly, something went terribly wrong.

Bombarded with security questions at a news conference, Virginia Tech President Charles Steger said authorities believed the shooting at the West Ambler Johnston dorm, first reported about 7:15 am (1215 GMT), was a domestic dispute and mistakenly thought the gunman had fled the campus.

"We had no reason to suspect any other incident was going to occur," he said.

The dormitory was locked down immediately after the shooting, Steger said, and a phone bank was activated to alert the resident advisers there so they could go door-to-door warning the 900 students in the dorm. Security guards deployed at the dorm, he said, and others began a sweep across campus.

Asked why he did not order a lockdown of the entire campus, Steger noted that thousands of nonresident students were arriving for 8 am (1300 GMT) classes, fanning out across the sprawling campus from their parking spots.

"Where do you lock them down?" Steger asked.

He said security on campus will be tightened now, but offered no details.

"We obviously can't have an armed guard in front of every classroom every day of the year," he said.

Overall, Steger defended the university's response, saying: "You can only make a decision based on the information you know at that moment in time. You don't have hours to reflect on it."

Some students were upset that the gunman was able to strike a second time, saying the first notification they got of the shootings came in an e-mail at 9:26 am (1326 GMT). The e-mail mentioned a "shooting incident" at West Amber Johnston, said police were investigating, and asked students to be cautious and contact police about anything suspicious.

Security experts not connected with Virginia Tech said their immediate questions focused on whether the university had adopted and practiced a plan to handle such dire crises, and whether its system of emergency communications was state-of-the-art.

It was second time in less than a year that the Virginia Tech campus was closed because of a shooting.

Last August, the opening day of classes was canceled and the campus closed when an escaped jail inmate allegedly killed a hospital guard off campus and fled to the Tech area. A sheriff's deputy involved in the manhunt was killed on a trail just off campus. The accused gunman, William Morva, faces capital murder charges.

As for other crime on campus, Virginia Tech reported just eight arrests for illegal weapons possession from 2003-05, according to statistics posted by the US Department of Education.

Calmly shooting

Though Steger did not explicitly say the student, who he identified as an Asian male, was also the gunman in the first shooting, he said he did not believe there was another shooter.

"We do know that he was an Asian male, this is the second incident, an Asian man who was a resident in one of our dormitories," said Steger in an interview with CNN, confirming for the first time that the killer was a student.

Two students told NBC television's "Today" show they were unaware of the dorm shooting when they reported to a German class where the gunman later opened fire.

Derek O'Dell, his arm in a cast after being shot, described a shooter who fired away in "eerily silence" with "no specific target, just taking out anybody he could."

After the gunman left the room, students could hear him shooting other people down the hall. O'Dell said he and other students barricaded the door so the shooter couldn't get back in, though he later tried.

"After he couldn't get the door open he tried shooting it open ... but the gunshots were blunted by the door," O'Dell said.

Investigators offered no motive, and the gunman's name was not immediately released.

The shooting began about 7:15 am on the fourth floor of the dorm.

Police were still investigating around 9:15 am, when a gunman wielding two handguns and carrying multiple clips of ammunition stormed Norris Hall, a classroom building a half-mile away on the other side of the campus.

At least 15 people were hurt in the second attack, some seriously. Many found themselves trapped after someone, apparently the shooter, chained and locked Norris Hall doors from the inside.

Students jumped from windows, and students and faculty carried away some of the wounded without waiting for ambulances to arrive.

Police commandos swarmed over the campus. A student used his cell-phone camera to record the sound of bullets echoing through a stone building.

Inside Norris, the attack began with a thunderous sound from Room 206, "what sounded like an enormous hammer", said Alec Calhoun, a 20-year-old junior who was in a solid mechanics lecture in a classroom next door.

Screams followed an instant later, and the banging continued. When students realized the sounds were gunshots, Calhoun said, he started flipping over desks to make hiding places. Others dashed to the windows of the second-floor classroom, kicking out the screens and jumping from the ledge of Room 204, he said.

"I must've been the eighth or ninth person who jumped, and I think I was the last," said Calhoun. He landed in a bush and ran.

Calhoun said that the two students behind him were shot, but that he believed they survived. Just before he climbed out the window, Calhoun said, he turned to look at his professor, who had stayed behind, apparently to prevent the gunman from opening the door.

The instructor was killed, Calhoun said.

Erin Sheehan, who was in the German class next door to Calhoun's class, told the student newspaper, the Collegiate Times, that she was one of only four of about two dozen people in the class to walk out of the room. The rest were dead or wounded, she said.

She said the gunman "was just a normal-looking kid, Asian, but he had on a Boy Scout-type outfit. He wore a tan button-up vest, and this black vest, maybe it was for ammo or something."

The gunman first shot the professor in the head and then fired on the class, another student, Trey Perkins, told The Washington Post. The gunman was about 19 years old and had a "very serious but very calm look on his face," he said.

"Everyone hit the floor at that moment," said Perkins, a second year student studying mechanical engineering. "And the shots seemed like it lasted forever."