The rampage began about 7:15 a.m. ET at West Ambler Johnston, a coeducational residence hall that houses 895 people. The gunman, armed with a 9-mm pistol and a .22-caliber handgun, killed two people there before making his way to Norris Hall, an engineering classroom building on the opposite end of the 2,600-acre campus.
About 9:15, the gunman chained the doors of the classroom building so his potential victims could not escape and police could not enter. There, he shot as many as 46 more people.
Not until 9:26 did the first warning to students and employees go out by e-mail, according to the time stamps on copies obtained by NBC News. By then, the classroom shooting was well under way.
The first e-mail had few details. It said: ?A shooting incident occurred at West Amber Johnston earlier this morning. Police are on the scene and are investigating.? The message warned students to be cautious and contact police about anything suspicious.
Maurice Hiller, a student, told The Associated Press that he went to a 9 a.m. class just two buildings away from the engineering building and that no warnings were coming over the outdoor public address system on campus at the time.
Steger said at a briefing for reporters that administrators and police initially believed the first shooting was an isolated domestic incident and did not see a need to close the university. Steger said they believed the gunman had fled the campus.