The 23-year-old South Korean gunman who committed the deadliest school shooting in US history was a disturbed, isolated man whose gory writings troubled his classmates and teachers.
Cho Seung-Hui moved to the United States when he was eight, and was in his final year of studying English at Virginia Tech where on Monday he gunned down at least 30 students before fatally shooting himself.
Authorities found few people on campus who knew Cho well, since he was a loner who rarely spoke in class and whose writings opened a window onto an unstable and violent mind.
"When I first heard about the multiple shootings ... my first thought was about my friends, and my second thought was 'I bet it was Seung Cho,'" said Ian MacFarlane, a former classmate of Cho's who posted two of the killer's plays online.
He was "a loner, obsessed with violence, and serious personal problems," MacFarlane said in an article on aol.com next to links to the two plays, "Richard McBeef" and "Mr Brownstone."
In the end, his writings may serve as his last testament and offer the only clues to his motive.
One of his plays describes a 13-year-old boy's escalating fight with his stepfather. "I hate him. Must kill Dick. Must kill Dick. Dick must die."
The boy stuffs a cereal bar down his stepfather's throat. Then, the elder man "lifts his large arms and swings a deadly blow".
The other play takes its name from the Guns 'N' Roses song "Mr. Brownstone," and tells of a crew of 17-year-olds who skip school to gamble at a casino and fantasize about killing their professor.
"Such an old constipated wicked man," says Joe. "I wanna kill him," says John.
"I wanna watch him bleed like the way he made us kids bleed," says Jane.
The writings were so shocking that a professor had pulled him from class, CNN reported.
"There were several of us in English who became concerned when we had him in class, for various reasons. And so I contacted some people to try to get some help for him because I was deeply concerned," Lucinda Roy, one of Cho's professors, said.
Stephanie Derry, who studied playwriting with Cho, told the school newspaper, Collegiate Times, that the gunman's dramas were "really morbid and grotesque" and that other students used to joke about his creepy work.
"It was his lack of behavior that really set him apart," Derry said. "He basically just kept to himself, very isolated."
ABC news and the Chicago Tribune reported Tuesday that Cho left a long, rambling note in his dormitory room, railing against "rich kids," "debauchery" and "deceitful charlatans" on campus.
"You caused me to do this," he wrote.
Cho also died with the words "Ismail Ax" in red ink on the inside of one of his arms, the Tribune reported, citing unidentified sources.
Police suspect Cho first killed two people at a campus dormitory, then returned to his own dorm to write the rambling invective, re-arm and then storm the classroom building where he chained shut the doors and stalked from room to room killing 30 people and himself.
Cho was among the 2,000 foreigners from more than 110 countries attending the 26,000-student university in Blacksburg, Virginia. Cho's family lived in Centreville, Virginia, a suburb of Washington.
The Tribune said his family runs a dry cleaning business while his sister graduated from the elite Princeton University.
South Korea's government expressed "indescribable surprise and shock" after Cho was identified.
Cho had shown recent signs of violent, aberrant behavior, including setting a fire in a dorm room and allegedly stalking some women, the Tribune said, citing an unnamed investigative source.
Investigators believe Cho at some point had been taking medication for depression, the daily said.
The lone gunman is the most common profile for a mass murderer, someone who is "isolated, reclusive and antisocial" said Alan Langlieb, director of workplace psychiatry at Johns Hopkins University.
"It's not exactly clear what snaps," he said. "Some of it is premeditated, but a person could wake up that day and decide, 'I'm going to create social havoc.'"