Virginia Tech Massacre

Todd said he wasn't surprised by Cho's rampage because "the main ingredients in our society that cause these shootings haven't changed."

Brian Rohrbough, whose 15-year-old son Daniel was killed at Columbine, used the anniversary of the massacre to call for release of a videotaped manifesto by Harris and Klebold that has long been sealed by local authorities for fear of encouraging copycats. Rohrbough said at a news conference that authorities could learn from the manifesto and might even have prevented the slaughter at Virginia Tech. "When information is uncovered and does not compromise the investigation it should be out there," he said. "I'm encouraged that the authorities in Virginia are being open with what they are learning."

Cho Seung-Hui, a Korean-born student who killed 32 people at Virginia Tech on Monday before committing suicide, referred to Harris and Klebold as "martyrs" in a written manifesto mailed to a TV network.

Broadcast of a video diatribe by the Virginia Tech gunman has reopened the debate over media use of vile or disturbing material that goes back decades to the likes of Son of Sam and the Zodiac killer.

Some media experts labeled the move as an effort to improve NBC ratings and questioned whether giving 23-year-old Cho an outlet for hate-filled rants served the public interest.

"It was a very bad decision," said Paul Levinson, chairman of the communication and media studies department at Fordham University. "He's not a public official, he's not a terrorist we are pursuing as part of our government policy. He's just an individual psycho."

The ethical breach comes when networks replay the footage to drive ratings, experts said. By taking that step, they run the risk of alienating the same advertisers they seek to attract.

Recent cases include video of Saddam Hussein's hanging in December and the beheading of Nick Berg, an American kidnapped by al Qaeda in 2004.