Cho Seung-hui took just nine minutes to kill 30 people at Virginia Tech in what was the worst massacre of its kind in the US, police have said.
Speaking at the final press conference on the massacre, Virginia Tech police chief Wendell Flinchum said that from the first emergency call at 09:42 local time, it took police officers about three minutes to reach the Norris Hall complex and a further five minutes to reach the second floor.
After using bolt cutters to break chains holding the hall's doors together, the officers made it to the classroom containing Cho, who had it shot himself among a number of his victims. Two handguns were found near his body.
Police confirmed that Cho had fired 170 rounds in Norris Hall during the nine-minute rampage and that staff and students had blocked the doors into classrooms to prevent the shooter from entering.
Mr Flinchum said: "I would like to take this chance to recognize the incredible acts of heroism by those first few officers on scene, and the students, staff and faculty inside Norris Hall.
"I have already described this as the most horrific scene we have ever encountered in our collective years in public safety. So, you can only imagine what those first officers came upon when they got to the second floor."
The investigation into the killings is ongoing and there is currently no evidence to link Cho to bomb threats made on the campus in the weeks prior to April 16th, when the shooting occurred.
Investigators have discovered that Cho purchased two handguns in the first three months of this year and practiced at local firing ranges.
There are still no links between Cho and the first two people who were shot in a dormitory room prior to the Norris Hall shootings. But tests have shown that one of the handguns used at the first scene was one of the two weapons used at the second scene at Norris Hall.
Videos which Cho sent to the US NBC network were made before the April 16th shootings, police said, although they were mailed between the two shootings.
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