BLACKSBURG, Va. - Virginia Tech students still on edge after the deadliest shooting in US history got another scare Wednesday morning as police in SWAT gear with weapons drawn swarmed Burruss Hall, which houses the president's office.

Virginia Tech students comfort each other as they mourn, holding candles on the Virginia Tech Drill field during a candlelight vigil, Tuesday, April 17, 2007, in Blacksburg, Va., in honor the victims of the April 16 shootings on Virginia Tech's campus. [AP]

The threat of suspicious activity turned out to be unfounded, said Virginia State Police spokeswoman Corinne Geller said, and the building was reopened. But students were rattled.

"They were just screaming, 'Get off the sidewalks,'" said Terryn Wingler-Petty, a junior from Wisconsin. "They seemed very confused about what was going on. They were just trying to get people organized."

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One officer was seen escorting a crying young woman out, telling her, "It's OK. It's OK."

Roommates and professors began opening up Wednesday about the gunman who had killed 32 people and himself in two university buildings on Monday. Roommates said Cho Seung-Hui rarely spoke or made eye contact with them and that his bizarre behavior became even less predictable in recent weeks.

Cho started waking up as early as 5:30 a.m. instead of his usual 7 a.m., his roommate, Joseph Aust, told ABC's "Good Morning America."

"I tried to make conversation with him earlier in the year when he moved in," Aust said. "He would just give one-word answers and stay quiet. He pretty much never looked me in the eye."

Aust was among many students and professors who described the killer in the worst shooting massacre in modern US history as a sullen loner, and authorities said he left a rambling note raging against women and rich kids.

News reports said that Cho, a 23-year-old senior majoring in English, may have been taking medication for depression and that he was becoming increasingly violent and erratic.

Professors and classmates were alarmed by his class writings - pages filled with twisted, violence-drenched writing.

"It was not bad poetry. It was intimidating," poet Nikki Giovanni, one of his professors, told CNN Wednesday. "At first I thought, OK, he's trying to see what the parameters are. Kids curse and talk about a lot of different things. He stayed in that spot. I said, 'You can't do that.' He said, 'Yes, I can.' I said, 'No, not in my class.'"

Giovanni said her students were so unnerved by Cho's behavior that she had security check on her room and eventually had him taken out of her class. Some students had stopped coming to class, saying Cho was taking photos of them with his cell phone, she said.

In screenplays Cho wrote for a class last fall, characters throw hammers and attack with chainsaws, said a student who attended Virginia Tech last fall. In another, Cho concocted a tale of students who fantasize about stalking and killing a teacher who sexually molested them.

"When we read Cho's plays, it was like something out of a nightmare," former classmate Ian MacFarlane, now an AOL employee, wrote in a blog posted on an AOL Web site.

"The plays had really twisted, macabre violence that used weapons I wouldn't have even thought of."

He said he and other students "were talking to each other with serious worry about whether he could be a school shooter."

Professor Carolyn Rude, chairwoman of the university's English department, said Cho's writing was so disturbing that he had been referred to the university's counseling service.

Despite the many warning signs that came to light in the bloody aftermath, police and university officials offered no clues as to exactly what set Cho off.

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