BLACKSBURG, Va. - The bloodbath lasted nine minutes - enough time for Seung-Hui Cho to unleash 170 rounds from his two pistols, or about one shot every three seconds.

During that time, Virginia Tech and city police spent three minutes dashing across campus to the scene. Then they began the agonizing process of breaking into the chained-shut building, which took another five minutes.

Once inside, as they sprinted toward the sounds of gunfire inside Norris Hall, Cho put a bullet through his head and died in a classroom alongside his victims.

A timeline of the rampage emerged yesterday as police provided new details about what they uncovered in the 10 days since Cho committed the worst mass shooting in modern U.S. history.

The five minutes police spent breaking into the building proved to be crucial. During that time, Cho picked off his victims with a hail of gunfire. He killed himself after police shot through the doors and rushed toward the carnage.

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 gotta be some sort of organization."

State Police Superintendent Col. 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 West Ambler Johnston dormitory, and why 18-year-old freshman Emily Hilscher was the first victim.

"We talk about possible motives and theories and whatnot, but we don't have any evidence to suggest anything," Flaherty said.

Police searched Hilscher's e-mails and phone records looking for a link. While Flaherty would not discuss exactly what police had found, he said neither Cho's nor Hilscher's records have revealed a connection.

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

Besides the 170 rounds Cho fired inside Norris, investigators found unused ammunition in the building, though Flaherty was unsure how much was found. Investigators have compiled 500 pieces of evidence from Norris Hall alone.

Virginia Tech Police Chief Wendell Flinchum said Cho had a class this semester in Norris Hall, although it was not scheduled to meet on the day of the rampage.

Flaherty cautioned that it could be months before the case is closed. The investigation will begin slowing down as authorities examine evidence, he said. *