Police in Virginia say the Cho Seung-Hui, who killed 32 people in a shooting rampage at Virginia Tech, sent photographs, a video and a multi-page manifesto to the US television network NBC.
NBC's flagship news programme, The Nightly News with Brian Williams, broadcast the video and even showed the express post envelope used by Cho to send his manifesto.
His package appeared to be sent between the two separate shooting incidents on Monday.
Police Superintendent Stephen Flaherty declined to give details about the documents, but a university official said they had been received by NBC in New York on Wednesday morning.
Two people, a male and a female, were killed in a student dorm in the first shooting and 30 people were killed, some of them executed at close range, in a classroom building on the campus about two hours later.
Supt Flaherty, speaking to reporters, said NBC had immediately handed the material over to the FBI.
Earlier, police said Cho Seung-Hui had been placed in a mental health facility for a time because of concerns that he was suicidal.
The move followed allegations of harassment made against him by two women of in 2005.
The South Korean-born student, 23, turned the gun on himself as police closed in on him on Monday.
At a news conference, police chief Wendell Flinchum said that Cho Seung-Hui had been put in a mental health facility under a temporary detention order in the autumn of 2005.
The Governor of Virginia, Tim Kaine, has set up an independent review into whether more could have been done to prevent the massacre.
The gunman has been described as a troubled loner whose behaviour had sometimes alarmed those around him.
The governor warned against making snap judgements and said he had 'nothing but loathing' for those who were making what he called a 'political hobby horse' of the killings.
US President George W Bush has said he now expects there to be renewed debate about gun control in the US following the deaths.
Mr Bush predicted there would be much discussion but insisted that this needed to wait until the facts of Monday's killings had been established.
Police said Cho Seung-Hui, a final year English literature student, had acted alone.
The South Korean cabinet held an emergency meeting to discuss the Virginia massacre early today.
Officials expressed fear about a possible racial backlash in the US, where South Koreans account for about 15% of foreign students
President Roh Moo-hyun extended his condolences to the victims, their families and the American people.
Meanwhile, police are still trying to establish a motive for the mass shooting and are examining plays written by Cho Seung-Hui.
