The gunman who massacred 32 people at Virginia Tech university was identified on Tuesday as a student from South Korea and a troubled loner whose behavior had sometimes alarmed those around him. As students and teachers grieved at a tearful memorial service led by President George Bush, police said Cho Seung-Hui (23) had acted alone.

Amid the horror at Virginia Tech were tales of heroism during the rampage, including an older professor — himself a Holocaust survivor — who gave his life to protect his students. Although he was 76, long past the usual retirement age, he was still teaching at Virginia Tech on Monday when chaos erupted in Norris Hall.

The gunman who killed 32 people and then himself at Virginia Tech university on Monday was identified by police on Tuesday as Cho Seung-Hui, a South Korean studying at the university. Police said Cho (23) was studying English literature. They gave no motive for the shooting rampage, the worst in United States history.

For the thousands of students on this sprawling campus in rural south-western Virginia, the worst threats early on Monday seemed to be an unusual bout of blustery weather and looming final exams. ”I was going over to grab something to eat,” said Aimee Fausser, an 18-year-old international studies student, describing her morning routine.

Police and university authorities faced pressure on Tuesday to explain how a gunman apparently evaded detection after killing two people and then went on to kill 30 others two hours later in America’s worst shooting rampage. The man, whom police have not identified, killed himself in a classroom at Virginia Tech university after opening fire on students and staff.