A fourth-year student from South Korea was behind the massacre of at least 30 people locked inside a Virginia Tech campus building in the deadliest shooting rampage in modern U.S. history, the university said Tuesday.
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 not 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.
South Korea's Foreign Ministry also expressed its condolences, saying there was no known motive for the shootings and that South Korea hoped the tragedy would not "stir up racial prejudice or confrontation."
"We are in shock beyond description," said Cho Byung-se, a ministry official handling North American affairs. "We convey deep condolences to victims, families and the American people."
He said Cho had been in the United States from a young age, but no further specifics were given.
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 could not 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.
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.
At least 20 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.