Amid widespread anger among survivors and relatives over the university's failure to lock down campus when a gunman was on the loose, investigators revealed they may have initially been pursuing the wrong man, US media reported.

Police said that during a more than two-hour gap between a first shooting Monday, in which a female and male student were killed, and the second in which 31 were killed, they were pursuing the boyfriend of the female victim, the New York Times reported.

The female victim's roommate "told the police that (Karl D.) Thornhill, a student at nearby Radford University, had guns at his town house," the newspaper said, quoting a police affidavit.

"The roommate told the police that she had recently been at a shooting range with Mr. Thornhill, the affidavit said, leading the police to believe he may have been the gunman," it said.

"But as they were questioning Mr. Thornhill, reports came in of widespread shooting at Norris Hall, making it clear that they had not contained the threat on campus," the Times wrote.

But as they questioned Thornhill, shooting was reported at the Norris Hall engineering building, the Times wrote.

The delay meant Cho apparently had ample time to return to his room, take weapons and ammunition and head to the engineering building where he chained doors shut from the inside before shooting dead 30 people then turning his weapon on himself.

Police search warrants said a bomb threat note was found in the vicinity of Cho's body which it was "reasonable to believe" he had authored. Cho was also carrying knives on him, and at least one more knife along with prescription medications for depression were found in Cho's room.

Police recovered a 9mm handgun and a .22 caliber hand gun from the crime scene.

Cho, who came to the United States from South Korea in 1992 when he was eight years old, reportedly also left behind a rambling note venting his rage and complaining about "rich kids."

"You caused me to do this," he wrote in the several-page-long note that also railed against "debauchery" and "deceitful charlatans."

Cho had shown recent signs of "violent, aberrant behavior," including stalking women and setting a fire in a dorm room, the Chicago Tribune said.

Fellow students in a playwriting class remembered the killer as a mostly silent classmate who wrote gory dramas in a juvenile tone.

"The plays had really twisted, macabre violence that used weapons I wouldn't have even thought of," wrote former classmate Ian MacFarlane who posted two of Cho's plays on aol.com.

"His writing, the plays, were really morbid and grotesque," student Stephanie Derry told the college newspaper, the Collegiate Times.

"He would just sit and watch us, but wouldn't say anything. It was his lack of behavior that really set him apart. He basically just kept to himself, very isolated," Derry said.

Victims of his rampage included a Holocaust survivor who barricaded the classroom door to allow his students to escape before finally being gunned down, as well as a pair of Lebanese students, an Indian engineering expert and a Canadian French teacher.

Just across from the building where the massacre took place, thousands of students, faculty and community residents lifted candles in unison in an hour-long ceremony after night fell Tuesday to honor those killed.

The slayings sent shudders around the world, especially in Seoul as shocked South Koreans came to terms with the news that the gunman was a compatriot.

President Roh Moo-Hyun called an emergency meeting of his aides for Wednesday.

Steve Flaherty, superintendent of state police, told reporters Cho had been living in a campus dormitory. He was a resident alien in the United States.

Larry Hincker, associate vice president for university relations, described Cho as a "loner."

The shooting immediately renewed concern over school security and access to guns that was rekindled last year by a rash of shootings. The state of Virginia has some of the weakest gun licensing requirements in the country.

Agence France-Presse