A puzzling start to a deadly day

Investigators, meanwhile, had tracked down Thornhill, pulling him over as he was driving off campus. He raised their suspicion at once by contradicting Haugh's account. His guns were not at his home, he said; he had taken them to his parents' house in Boston, Va., about 370 miles away. He also denied that he and Hilscher had spent the weekend at Longwood University in Farmville, about 140 miles from Blacksburg.

Campus Police Det. Stephanie Henley requested a search warrant for a residence believed to be linked to Thornhill. She was looking, she wrote, for "firearms, ammunition, bloody clothing ... "

Murky motive

Authorities are as yet unwilling to clear Thornhill; he "remains a person of interest," according to the state police superintendent, Col. Steven Flaherty.

But Flaherty also said it's "reasonable to assume" that Cho committed the murders at Ambler Johnston Hall. Why he may have targeted that dorm, that room, is murky. There's no evidence that he knew Hilscher. He was a 23-year-old English major, a taciturn loner; she was an upbeat 19-year-old studying animal sciences, so close to her family that she called her mother every day.

If Cho had planned a massacre, he had ample opportunity to shoot other victims; the dorm was filled with sleeping students. But only one other student, 22-year-old senior Ryan Clark, was shot in the dorm, known as AJ. Then the gunman fled.

Nearly 2 1/2 hours later, Cho turned up in Norris Hall, a science and engineering building half a mile from AJ. He was armed with two handguns, one of them the weapon used to kill Hilscher and Clark in the dorm.

His face was still, expressionless, as he methodically began to kill.

'Unremarkable' gun sale

Cho bought one gun, a .22-caliber Walther P22, in February, at a pawnshop on Main Street.

The other he purchased March 12 at Roanoke Firearms, about 40 miles away.

The gun shop is in a cream-colored brick building, set up against the Blue Ridge Mountains, with the words: "Protection -- Service -- Training" etched on the door. Inside, guns of every description, price tags dangling, are displayed in glass cases. A bumper sticker on the wall urges: "Buy a gun for America."

Cho bought a Glock 9-millimeter pistol here for $535, 30 rounds of ammunition included.

As required by law, he presented identification: a Virginia driver's license, checks that matched the address on the license, and a federal immigration card to prove he was a legal U.S. resident. He passed a background check and left the store with his gun.