The first crackle of gunfire shattered the Monday morning calm. It was 7:15 a.m. on the campus of Virginia Tech and an epic killing spree had just begun.

Snow was swirling on the windy April day and classes had not yet started when a murderous rampage that would shake the nation started in a coed dormitory, West Ambler Johnston, home to 895 students.

The first reports of trouble were tragic, but small in scope, no hint of the massacre about to unfold in the Blue Ridge mountains of Virginia: One person was dead, another injured.

The official word to students apparently did not come right away.

In a mass e-mail, Virginia Tech officials announced a shooting had occurred at the dorm, police were on the scene and urged anyone in the university community to “be cautious” and contact police if they saw anything suspicious or had information on the case.

The e-mail was signed off at 9:26 a.m.

Police would later say they thought the two had been shot in a domestic dispute. They thought the gunman had fled the campus.

“We secured the building, we secured the crime scene,” Virginia Tech Police Chief Wendell Flinchum said. For a long while, there were no new reports of anything suspicious.

Classes on the Blacksburg, Va., campus had gone ahead as schedule; the first period began at 8 a.m. The doors of the buildings remained open. And the heavily armed gunman with a motive yet unknown had set his sights elsewhere, at Norris Hall, an engineering building nearly a half-mile away on the 26,000-acre campus.

Police believe the shooting at Norris began around 9:45 a.m. The building’s doors had been chained shut, possibly by the gunman, authorities said.

At 9:55 a.m, the school sent out a second e-mail.

“Please stay put,” it warned. “A gunman is loose on campus. Stay in buildings until further notice. Stay away from all windows.”

Soon after, horrifying sounds and images flooded TV screens and Internet sites across America. SWAT teams in flak jackets swarmed the campus. Students helped faculty members carry out the wounded, as ambulances streamed to the site.

CNN showed a jerky video provided by a student’s cell phone that showed what seemed to be police outside Norris Hall accompanied by a chilling soundtrack — the crackle of gunshots.

What had happened inside? Reports were fragmentary.