"The world has endured a view of life that few of us would or should ever have to endure"
Virginia police chief
On Thursday relatives of Cho's victims who had been scheduled to appear on NBC cancelled their interviews to protest against the broadcasting of the videos.
Police investigating the shootings in Blacksburg, Virginia, also criticised the airing of the manifesto.
"We're rather disappointed in the editorial decision to broadcast these disturbing images," Colonel Steve Flaherty, the Virginia state police chief, said.
"The world has endured a view of life that few of us would or should ever have to endure."
In the package sent to NBC, Cho, a 23-year-old student, included photographs of himself posing with his guns and videos railing against rich students and what he said was debauchery on campus.
"With hundreds of millions of guns kicking around this country... incidents like this will continue to happen"
Dave, Bisbee, US
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"You forced me into a corner and gave me only one option," he said at one point in the video. "This didn't have to happen."
The package to NBC News was mailed after he killed his first two victims on Monday morning but before he cut down 30 more in classrooms.
Cho eventually turned his gun on himself.
Amid the criticism at NBC, other major US broadcasters also said they would limit airing of footage from Cho's video.
ABC News reduced its coverage to showing still excerpts from the video or muting the audio, but left video images on its website.
"Once you've seen it, its repetition is little more than pornography once that first news cycle is passed," Jeffrey Schneider, senior vice-president of ABC News, said.
|Virginia Tech campus remains in shock |
after Monday's shootings [Reuters]
A spokeswoman for CBS News said the broadcaster would use the images "only when necessary to tell the story".
"The bar is set very high. I would be surprised to see much usage of it," she said.
Fox News said "we see no reason to continue assaulting the public with these disturbing and demented images", although it said it would reserve the right to use them as needed in the future.
NBC acknowledged that the images were probably devastating to the victims' families.
However, Steve Capus, the president of NBC News, defended the decision to air the material and said other news outlets around the world also broadcast it.
"This is I think as close as we will ever come to being inside of the mind of a killer, and I thought that it needed to be released," Capus told cable network MSNBC.
NBC said it contacted the authorities as soon as it received the package on Wednesday and took "careful consideration" in determining how to use the information.
"Our standards and policies chief reviewed all material before it was released," NBC said in a statement.