Witnesses place Cho outside the West Ambler Johnston dorm shortly before 7:15 a.m., when he fired the two shots that killed Hilscher and 22-year-old senior Ryan Clark, a resident assistant at the dorm, Flaherty said.
It is not known how Cho got in.
Police searched Hilscher's e-mails and phone records looking for a link. While Flaherty would not discuss exactly what police 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."
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.
Associated Press writers Matt Apuzzo and Chris Kahn in Blacksburg, Pat Milton in New York, and Nicholas K. Geranios in Spokane, Wash., contributed to this report.