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Despite Cho's inner turmoil, he carried out his last acts with calm determination.

He sent bomb threats to school officials, authorities believe.

He chained the doors on Norris Hall and brought along enough ammunition to kill 50.

Police also said he tried to shave the serial numbers off his new Walther P22 and 9-millimeter Glock, both heavy handguns.

And he carried no identification.

In his final moments, shooting point-blank at students and professors, firing through doors at others who tried to barricade themselves from him, he seemed never to lose his nerve, often reloading.

He hit many people three or more times at close range.

"I'm sure the behavioral people will be looking into what it was that set this kid off," said a federal law enforcement official familiar with the investigation.

The first attack occurred at 7:15 a.m., when Emily Hilscher, a student, and Ryan Clark, a resident advisor, were shot to death at the West Ambler Johnston dorm.

Hilscher's roommate, Heather Haugh, said her friend did not know Cho and she knew no reason he would first turn his violence upon her.

"I've never seen him," she said.

"I don't know his name.

Emily didn't know him, as far as I know." She said that speculation about a domestic dispute probably stemmed from the fact that she told police that Hilscher's...

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