Sheree Mixell, a spokeswoman for the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, said the evidence was being moved to the agency's national lab in Annandale. At least one firearm was turned over, she said.

Mixell would not comment on what types of weapons were used or whether the gunman was a student.

Students jumped from windows in panic. Young people and faculty members carried out some of the wounded themselves, without waiting for ambulances to arrive. Many found themselves trapped behind chained and padlocked doors. SWAT team members with helmets, flak jackets and assault rifles swarmed over the campus. A student used his cell-phone camera to record the sound of bullets echoing through a stone building. Alec Calhoun, a 20-year-old junior, said he was in a 9:05 a.m. mechanics class when he and classmates heard a thunderous sound from the classroom next door — "what sounded like an enormous hammer."

Screams followed an instant later, and the banging continued. When students realized the sounds were gunshots, Calhoun said, he started flipping over desks for 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, of Waynesboro, Va. 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 the professor, who had stayed behind, perhaps to block the door.

The instructor was killed, he said.

Trey Perkins, who was sitting in a German class in Norris Hall, told The Washington Post that the gunman barged into the room at about 9:50 a.m. and opened fire for about a minute and a half, squeezing off 30 shots in all.

The gunman, Perkins said, first shot the professor in the head and then fired on the students. Perkins said the gunman was about 19 years old and had a "very serious but very calm look on his face."

"Everyone hit the floor at that moment," said Perkins, 20, of Yorktown, Va., a sophomore studying mechanical engineering. "And the shots seemed like it lasted forever."

Erin Sheehan, who was also in the German class, told the student newspaper, the Collegiate Times, said 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."