A man and woman were shot dead at the dormitory

An emergency call to attend a dormitory room in West Ambler Johnston Hall is received by Virginia Tech Police Department (VTPD), the college's own police unit.

Officers find a man - Ryan Clark, 22 - and a woman - Emily Hilscher, 19 - shot dead in a fourth-floor room.

At the time the shootings are believed to be an isolated, domestic incident.

Police seal off the hall, home to about 900 students, and tell students to stay indoors.

Emily Hilscher and Ryan Clark were the first victims

Blacksburg police help to establish a safety perimeter and close nearby Washington Street.

Officers question students and, by 0730, a "person of interest" is being investigated.

At 0825 senior university staff meet to assess what is happening and how to tell students.

At 0900 the leadership team is briefed by the campus police chief.

Cho sent a bundle of 'disturbing' images and writings

Amid the shock and chaos on campus, the man later identified as Cho Seung-hui is posting a package of "disturbing" material to a US television station.

The package, which was not opened for another two days, contains photographs, video clips and documents.

They include rantings directly at the camera, photographs of him pointing guns and a 1,800-word written diatribe.

On one clip he declares: "Now you have blood on your hands."

Cho takes the package, containing a total of 23 video clips and 29 photographs, to the post office in Blacksburg's North Main Street, for delivery to NBC News president Steve Capus.

Shootings took place at Norris Hall

About two hours after the first shootings, the gunman opens fire again.

The attack takes place at Norris Hall, an engineering complex containing offices, classrooms and laboratories.

The building is about half a mile (800 metres) from West Ambler Johnston Hall, on Virginia Tech's sprawling campus.

University officials send an e-mail to all staff and students, saying there has been a shooting at West Ambler Johnston Hall and police are investigating.

VIRGINIA TECH FACTS More than 25,000 full-time students More than 100 buildings 1,000 hectares (2,600 acres) Campus includes an airport Largest full-time student population in Virginia Source: Virginia Tech

"The university community is urged to be cautious and are asked to contact Virginia Tech Police if you observe anything suspicious or with information on the case."

Information is also circulated via emergency telephone messages and on the college website.

By this time, the second shootings have begun at Norris Hall.

Police had to force their way in to Norris hall

Virginia Tech police receive a call about the second shootings - at Norris Hall.

Campus and Blacksburg officers attend and find the front doors chained from the inside.

They force their way in and follow the sound of gunshots to the second floor.

At least 15 people were injured

As police reach the second floor of Norris Hall, the shooting stops. There is no exchange of fire with the gunman.

"The gunman was discovered among several of the victims in one of the classrooms. He had taken his own life," police say later.

The death toll at Norris Hall is confirmed as 30, plus the gunman. At least 15 more are wounded. Victims are found in at least four classrooms and a stairwell.

Staff and students were devastated

College officials send another e-mail to all staff and students.

The second e-mail is sent around the time of the second shootings.

It says: "A gunman is loose on campus. Stay in buildings until further notice. Stay away from all windows."

Cho Seung-hui was a student at Virginia Tech

Another e-mail advises everyone that all classes are cancelled and those on campus should "remain where they are, lock their doors and stay away from windows." Those not already on site should stay away.

The gunman is later named as Cho Seung-hui, a 23-year-old South Korean student at the university and a resident in Harper Hall, another dormitory on the campus.

Two handguns are found at Norris Hall. Police say one of the weapons was used in both shootings.

Police say it is "reasonable to assume" that Cho was the gunman in both incidents, but they are not yet ruling out the possibility of a second person's involvement.

Around 30 people are initially taken to hospitals in the area, of which a dozen remain 48 hours later.