Cho Seung-Hui, the student who killed more than 30 people at Virginia Tech university sent a "multimedia manifesto" to US network NBC News in the midst of his shooting spree. Virginia police superintendent Steve Flaherty said the package containing photographs, video and writings could be a "very new critical component" of the investigation.
The correspondence is believed to have been sent after the first shooting in the university dormitory, in which two students were killed, but before Cho shot dead another 30 people in a classroom across campus.
NBC News said the correspondence contained "a rambling communication and videos about his grievances". The contents, which were not disclosed, were described as "disturbing". Col Flaherty said: "We're in the process of attempting to analyse and evaluate its worth."
It emerged yesterday that Cho was questioned by police and admitted to a psychiatric hospital in 2005 after he was accused of stalking two women students. Campus police chief Wendell Flinchum said yesterday that in November and December 2005, two women complained that they had received calls and "annoying" computer messages from Cho.
"I'm not saying they were threats, I'm saying they were annoying. That's the way the victims characterised them, as annoying messages," Mr Flinchum said. In the first instance, Cho reportedly telephoned a female student and made direct contact with her. Police spoke to Cho after she lodged a complaint, they said.
In a similar incident a month later, in December 2005, Cho reportedly made contact with another female student through instant messaging, leading to her complaint.
The women, neither of whom were among those shot this week, did not press charges but after the second complaint, the university obtained a temporary detention order and sent Cho to Carilion St Alban's Hospital for psychiatric evaluation.
The examination found that Cho had a "flat" effect but concluded that his judgment did not seem to be impaired. "He denies suicidal ideations. He does not acknowledge symptoms of a thought disorder. His insight and judgment are normal," it said.
Police said they found prescription medicines for treating psychological disorders among Cho's belongings but they did not give details of the drugs found. The disclosure about his psychiatric history has fuelled criticism of the university authorities for failing to identify Cho as dangerous and for waiting more than two hours before warning students after the first of Monday's two gun attacks. After student Emily Jane Hilscher and Ryan Clark, a college adviser, were shot dead in a dormitory building, the campus police began searching for Ms Hilscher's boyfriend, Karl Thornhill.
Ms Hilscher's room-mate had told police that Mr Thornhill had guns at his house and had recently visited a shooting range. While they were questioning Mr Thornhill police heard about the shootings at Norris Hall.
- (addition reporting Reuters)