BLACKSBURG, Va. -- The Virginia Tech gunman started his day of mayhem lurking outside a dormitory before 7 a.m. Moments later, he sneaked inside and shot his first two victims with two lethal rounds from a 9 mm pistol.
The next wave of carnage involved much more firepower. Police said he unleashed 170 rounds on the classrooms of Norris Hall during a nine-minute rampage. Thirty people were killed in the building; more were wounded.
During that spree, police spent three minutes rushing to the building and then about five minutes carrying out the complicated process of breaking through the building's doors, which Seung-Hui Cho had chained.
A timeline of Cho's morning and the final moments of his life emerged Wednesday during a news conference by police who are still struggling to figure out why the 23-year-old student carried out the rampage.
The five minutes police spent breaking into the building proved to be crucial as Cho moved through Norris Hall unimpeded, with police locked out.
Authorities eventually blew their way into the building, and as they began to rush toward the gunfire on the second floor, Cho put a bullet through his head and died, surrounded by his victims.
State police spokeswoman Corinne Geller praised the officers' response time, noting that had police simply rushed into the building without a plan, many would have likely died right along with the staff and students. She said officers needed to assemble the proper team, clear the area and then break through the doors.
"If you go in with your backs turned, you're never going back," Geller said. "There's got to be some sort of organization."
Some police and security experts question the five-minute delay, saying authorities should have charged straight into the melee.
"You don't have time to wait," said Aaron Cohen, president of IMS Security of Los Angeles, who has trained SWAT teams around the country since 2003. "You don't have time to pre-plan a response. Even if you have a few guys, you go."
After the Columbine massacre in 1999, police around the country adopted new policies for so-called "active shooters." Police would no longer respond to emergencies such as school shootings by surrounding a building and waiting for the SWAT team.
Instead, the first four officers rush into the building and attempt to immediately end the threat. This system was used to end a 2003 school hostage standoff in Spokane, Wash.
At Columbine, no officers entered the building until about 40 minutes after the first 911 call from the school. Critics have said that decision might have contributed to the death of a teacher who bled to death from gunshot wounds.
Tom Corrigan, former member of a terrorism task force and a retired New York City detective, said five minutes seems like a long time when gunfire is being heard, but he added it's tough to second-guess officers in such a chaotic situation.
"I would have liked to have seen them bust down the door, smash windows, go around to another door, do everything to get inside fast," he said. "But it's a tough call because these officers put their lives on the line on a daily basis and I am sure they did the best they could."
Al Baker, a former 25-year veteran in the New York Police Department, echoed that sentiment, but said sometimes officers have to do whatever is necessary to enter a building - whether it's throwing a rock through a window or driving a car through the door. He said the crucial issue is ensuring that officers have the proper training and equipment.
"This is a seminal moment for law enforcement as far as I'm concerned because it proves that minutes are critical," he said.
State Police Superintendent Col. W. Steven Flaherty, who is overseeing the investigative team looking at the shootings, said police have been unable to answer the case's most vexing questions: Why the spree began at the dormitory, and why 18-year-old freshman Emily Hilscher was the first victim.