A fourth-year student from South Korea carried out the massacre of at least 30 people locked inside a Virginia Tech campus building in the deadliest shooting rampage in modern U.S. history.
Ballistics tests also found that one of the guns used in that attack was also used in a shooting two hours earlier at a dorm that left two people dead, Virginia State Police said.
Police identified the shooter as Cho Seung-Hui, 23, a senior in the university's English department who lived on campus. Authorities said he was a legal resident of the United States. Cho committed suicide after the attacks, and there was no indication Tuesday of any possible motive.
"He was a loner, and we're having difficulty finding information about him," school spokesman Larry Hincker said.
Two law enforcement officials, speaking on condition of anonymity because the information had not been announced, said Cho's fingerprints were found on the guns used in the shootings. The serial numbers on the two weapons had been filed off, the officials said.
One law enforcement official said Cho was carrying a backpack that contained receipts for a March purchase of a Glock 9 mm pistol.
Col. Steve Flaherty, superintendent of the Virginia State Police, said it was reasonable to assume that Cho was the shooter in both attacks but that link was yet definitive.
"There's no evidence of any accomplice at either event, but we're exploring the possibility," he said.
A memorial service was planned at the university later Tuesday, and President George W. Bush planned to attend, the White House said. Gov. Tim Kaine was flying back to Virginia from Tokyo for the 2 p.m. (1800 GMT) ceremony.
The first deadly attack, at a dormitory around 7:15 a.m., left two people dead. But some students said they did not get their first warning about a danger on campus until two hours later, in an e-mail at 9:26 a.m. By then the second attack had begun.
Two students told NBC's "Today" show they were unaware of the dorm shooting when they walked into Norris Hall for a German class where the gunman later opened fire.
The victims in Norris Hall were found in four different classrooms and a stairwell, Flaherty said. Cho was found dead in one of those classrooms, he said.
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.
A federal law enforcement official said Tuesday he had been told by other federal law enforcement officials that the two guns recovered in the shooting had had their serial numbers scraped off. The official spoke on condition of anonymity because the information had not been announced.
The slayings left people of this once-peaceful mountain town and the university at its heart praying for the victims and struggling to find order in a tragedy of such unspeakable horror it defies reason.
"For Ryan and Emily and for those whose names we do not know," one woman pleaded in a church service Monday night.
Another mourner added: "For parents near and far who wonder at a time like this, 'Is my child safe?"'
That question promises to haunt Blacksburg long after Monday's attacks.
The shooting began about 7:15 a.m. on the fourth floor of West Ambler Johnston, a high-rise coed dormitory where two people died.
Police were still investigating around 9:15 a.m., 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 2,600-acre (1,052-hectares) campus.
At least 26 people were taken to hospitals after the second attack, some seriously injured. 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 near Calhoun's room, 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, 20, a second-year mechanical engineering student. "And the shots seemed like it lasted forever."
At an evening news conference, Police Chief Wendell Flinchum refused to dismiss the possibility that a co-conspirator or second shooter was involved. He said police had interviewed a male who was a "person of interest" in the dorm shooting and who knew one of the victims, but he declined to give details.
Some students bitterly complained that the first e-mail warning arrived more than two hours after the first shots.
"I think the university has blood on their hands because of their lack of action after the first incident," said Billy Bason, 18, who lives on the seventh floor of the dorm.
University President Charles Steger emphasized that the university closed off the dorm after the first attack and decided to rely on e-mail and other electronic means to spread the word, but said that with 11,000 people driving onto campus first thing in the morning, it was difficult to get the word out.
He said that before the e-mail was sent, the university began telephoning resident advisers in the dorms and sent people to knock on doors. Students were warned to stay inside and away from the windows.
"We can only make decisions based on the information you had at the time. You don't have hours to reflect on it," Steger said.
The 9:26 e-mail had few details: "A shooting incident occurred at West Amber Johnston earlier this morning. Police are on the scene and are investigating."
Until Monday, the deadliest shooting in modern U.S. history was in Killeen, Texas, in 1991, when George Hennard plowed his pickup truck into a Luby's Cafeteria and shot 23 people to death, then himself.
Nine students remained hospitalized Tuesday at Montgomery Regional Hospital, all of them stable, CEO Scott Hill said. Two others had been transferred to other hospitals with a Level I trauma center.
Their families "are by the bedside, which is a good thing," Hill said.
Lewis-Gale Medical Center in Salem had three remaining patients, all in stable condition, with one expected to be discharged later Tuesday, Hill said.
The massacre Monday took place almost eight years to the day after the Columbine High bloodbath near Littleton, Colorado. On April 20, 1999, two teenagers killed 12 fellow students and a teacher before taking their own lives.
Previously, the deadliest campus shooting in U.S. history was a rampage that took place in 1966 at the University of Texas at Austin, where Charles Whitman climbed the clock tower and opened fire with a rifle from the 28th-floor observation deck. He killed 16 people before he was shot to death by police.
Founded in 1872, Virginia Tech is nestled in southwestern Virginia, about 160 miles (257 kilometers) west of Richmond. With more than 25,000 full-time students, it has the state's largest full-time student population. The school is best known for its engineering school and its powerhouse Hokies football team.
Police said there had been bomb threats on campus over the past two weeks but that they had not determined whether they were linked to the shootings.
It was second time in less than a year that the campus was closed because of gunfire.
Last August, the opening day of classes was canceled when an escaped jail inmate allegedly killed a hospital guard off campus and fled to the Tech area. A sheriff's deputy was killed just off campus. The accused gunman, William Morva, faces capital murder charges.
Among the dead were professors Liviu Librescu and Kevin Granata, said Ishwar K. Puri, the head of the engineering science and mechanics department.
Librescu, an Israeli, was born in Romania and was known internationally for his research in aeronautical engineering, Puri wrote in an e-mail to The Associated Press.
Granata and his students researched muscle and reflex response and robotics. Puri called him one of the top five biomechanics researchers in the country working on movement dynamics in cerebral palsy.
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