Campus gunman 'fired 170 bullets'

Virginia Tech gunman Cho Seung-hui fired more than 170 bullets in nine minutes in the rampage that killed 30 students and staff, police have said.

One of the guns fired was also used to kill two students two hours earlier.

Giving an update on the investigation 10 days after the campus shootings, police said they still had no evidence on Cho's specific motives for his acts.

But they have concluded the video clips he posted to NBC News between the two shootings were not filmed that day.

The disturbing footage, accompanied by ranting writings and photographs of Cho with weapons, was received by the news broadcaster two days later.

Police confirmed the 23-year-old South Korean-born gunman shot himself in the head in one of the classrooms in the Norris Hall complex after the nine-minute shooting spree.

'Frustrating'

Virginia's state police superintendent, Col Steve Flaherty, told a press conference in Blacksburg that police had been examining 500 pieces of evidence taken from Norris Hall.

Officers have also examined hundreds of mobile phone, e-mail and computer records in the search for clues to Cho's motivation.

So far, no close links have been found between Cho and any of his victims, Col Flaherty said.

"We certainly don't have any one motive that we are pursuing at this particular time, or that we have been able to pull together and formulate," he said.

"It's frustrating because it's so personal, because we see the families and the communities suffering, and we see that they want answers."

The shootings began when two people were killed at the West Ambler Johnston Hall, a university dormitory, at 0715 on Monday.

Despite confirming that one of the handguns found with Cho was used in that incident and that he had been seen outside the dormitory just before 0700, police have not declared categorically that he was responsible.

"We are still trying to figure out what he did or did not do," said campus police chief Wendell Flinchum.

Bomb threats

Police confirmed that when they were called to reports of gun fire across campus at Norris Hall two hours later, they found three entrance doors chained shut.

They said they had established where Cho had bought the chains, ammunition and guns used in the shootings but did not reveal the details.

There was no evidence to link him to bomb threats made on campus in previous weeks, they added.

Speaking to the Associated Press, Col Flaherty warned that the investigation could take months.

An independent six-member panel has also been asked to examine the day's events and the treatment Cho received for mental health problems before the shooting.

Students returned to classes at the university on Monday, when a ceremony was held to commemorate the victims.