Cho never lived at West AJ, as the towering dorm was called. He had no friends there, as far as anyone knows. And yet a room on the fourth floor was the spot where the 23-year-old senior chose to start the deadliest one-man shooting spree in modern U.S. history.

Why? Was he fixated on someone who lived there, or was it the place itself? And why did he choose to complete his rampage across campus in the classrooms of Norris Hall?

"The why and the how are the crux of the investigation," Virginia State Police spokeswoman Corinne Geller said Friday. "The why may never be determined because the person responsible is deceased."

So far, investigators in the Virginia Tech massacre that left Cho and 32 other people dead have divulged no connection between Cho and the first two victims, Emily Hilscher and resident adviser Ryan Clark. Both were gunned down at West AJ.

"We're trying to establish those links, if there are any," Geller said.

Police filed a search warrant for Hilscher's laptop and cell phone, saying in court papers that Cho might have communicated with her via computer.

FBI behavioral profilers are among those trying to understand Cho's motives.

CLUES COULD COME FROM NBC PACKAGE

Clues about Cho's possible motives could come from the writings, photographs and video footage that Cho mailed to NBC. Cho rages against rich kids, snobs and those who wronged him. Cho also left behind an eight-page letter, and a typed, single-spaced page, shown Friday to The Associated Press, makes some of the same points.

"You pick out the Weak and the Defenseless and turbo-(expletive deleted) us for your own pleasure and put on faces of devout Christians in front of your parents and strangers," it read. "You drink your vodka, share needles and go on your escapades on Saturday night and go to church on Sunday morning."

He added: "You have to search high and low for the Weak and the Defenseless to taunt and terrorize on Monday."

While Cho was obviously seething with anger and fantasies of violence long before the rampage, it is not clear exactly what set him off on Monday.

One possible clue: The attack took place nearly eight years to the day after the Columbine High massacre in Colorado that left 15 people dead on April 20, 1999. In the video rant that Cho mailed off to NBC in the middle of the rampage, he expressed admiration for the teenage killers at Columbine, Eric Harris and Dylan Klebold.

Classmates in Virginia, where Cho grew up, said the South Korean immigrant was teased and picked on, apparently because of shyness and his strange, mumbly way of speaking. Among the victims of the massacre were two young women who graduated from Cho's high school. But investigators said it is not clear whether Cho targeted them.

POSSIBLE CONNECTIONS TO TARGETED BUILDINGS

Koch said Cho — who became known as the "question mark" after he scrawled a question mark on a sign-in sheet on the first day of a literature class — had a possible connection to West AJ.

At least three women have said they received unwanted advances from Cho, either in the form of bizarre computer messages or a question mark scrawled on a dry-erase board on a dorm room door. Two of the women complained to campus police, and Koch said the first lived in West AJ.

Another mystery: Why did the English major target Norris, a building dominated by engineering and foreign language classes? Chris Davids, a Virginia Tech senior who went to high school with Cho, said he remembers seeing Cho on campus a lot freshman year, and concluded that Cho, like him, started out as an engineering major.

"If he started in engineering and had to switch to English that might be a reason why he's angry at the engineering department," Davids said.