From the AP, on the continuing motivation of Seung-Hi Cho's murderous shooting spree:

In an interview Tuesday with The Associated Press, State Police Superintendent Col. W. Steven Flaherty said authorities have found no evidence that could begin to explain the massacre that ended when Cho took his own life.

Authorities also have no link between the 23-year-old loner and his victims.

"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."...

Flaherty, who is overseeing the investigative team looking at the shootings, said police also have been unable to answer one of the case's most vexing questions: Why the spree began at the West Ambler Johnston dorm, and why 18-year-old freshman Emily Hilscher was the first victim.

Police have 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.

Flaherty said there was also no link to 22-year-old senior Ryan Clark, who was also killed at the dorm. Nor do investigators know why Cho, an English major, selected Norris Hall - a building that is home primarily to engineering offices - to culminate his attack. Cho killed 30 people there before taking his own life.

More here.

I'm guessing that they will never find a "motive" in any clean, easily comprehended sense of the term. This was madness, for lack of a better term, and even as we might come to understand what pushed Cho's buttons, there's simply no sufficient explanation for his actions.