Reporters continued to ask today why administrators did not cancel classes after the first shooting, and why it took more than two hours to inform the university community via e-mail about the first incident. The first e-mail notifying students of the dorm shooting was not sent by the school until 9:24 a.m -- by which time the second shooting was already over.
According to President Charles Steger, the administration locked down West Ambler Johnston Hall dormitory after the first shooting. But he said classes weren't canceled because the shooting was believed to be tied to a domestic dispute and campus police believed the shooter had left the campus.
"The second shooting, no one predicted that was also going to happen that morning," Steger said. "So if you're talking about locking it down, what is it you're going to lock down? It's like closing a city. It doesn't happen simultaneously."
By Monday night, investigators had ruled out the possibility of a murder-suicide in the first dormitory shooting. Ryan "Stack" Clark, a member of the school's marching band, the Marching Virginians, and a student resident assistant, was killed there by a shot in the neck. His next-door neighbor, freshman Emily Hilscher, was also found dead.
At Norris Hall, the gunman left a trail of bloodshed, which Flinchum, the Virginia Tech police chief, called "one of the worst things I've seen in my life."
Cho apparently shot himself in the head after the killings; part of his face was missing when his body was found.
Police documents today showed authorities suspected Cho may have been the source of two bomb threats last week targeting Virginia Tech engineering buildings.
The first of the two threats was directed at Torgersen Hall, a classroom and laboratory building, while the second was directed at multiple engineering buildings. Students and staff were evacuated, and the university sent out e-mails across campus, offering a $5,000 reward for information about the threats.
Virginia Tech -- formally known as Virginia Polytechnic Institute and State University -- is located in the western end of the state near the borders of West Virginia and Tennessee. It has more than 25,000 full-time students. Its campus, which spreads over 2,600 acres, has more than 100 buildings.
The number of dead is almost twice as high as the previous record for a mass shooting on an American college campus. That took place at the University of Texas at Austin on Aug. 1, 1966, when a gunman named Charles Whitman opened fire from the 28th floor of a campus tower. Whitman killed 16 and injured 31.
ABC News' Amy Thomas and Jason Ryan contributed to this report.