BLACKSBURG, Virginia - A videotaped diatribe by the Virginia Tech gunman shocked victims' families and mesmerized television viewers, but police said on Thursday it yielded little for their investigation of the campus massacre.

A Virginia Tech faculty member lays a flower at a memorial to the victims of the Virginia Tech shooting, on the campus in Blacksburg, Virginia April 19, 2007. [Reuters]

Still grieving, students at the university expressed disgust at self-made photos and a disturbing video the killer mailed to NBC News on Monday when he paused during the deadliest shooting rampage in modern US history.

Police handling the investigation criticized the airing from Wednesday evening of the images and rants by Cho Seung-Hui, who killed 32 people and then himself at the sprawling campus in southwestern Virginia.

State police chief Steve Flaherty said victims' families and the Virginia Tech community had been badly struck not only by tragedy but by the intense media attention surrounding it.

Cho's video manifesto brandishing guns and ranting at times incoherently drew wall-to-wall US news coverage.

"The world has endured a view of life that few of us would or should ever have to endure," Flaherty told a news conference. "I'm sorry you all were exposed to these images."

Campus authorities have also faced questions after it emerged that they had become aware of Cho's troubled mental state 17 months before he went on his killing spree.

University officials insisted they had no responsibility for monitoring Cho's psychiatric care after he was said to have been suicidal in 2005 and was sent to a mental health center.

Virginia Gov. Tim Kaine announced the makeup of a panel, including former Homeland Security Secretary Tom Ridge, to look into the university's response to the shootings, after it was criticized for being slow to warn students of the danger.

'LITTLE MORE THAN PORNOGPRAHY'

With Cho's imbalance displayed in his video manifesto, families of victims were so upset at NBC's decision to air the images that they canceled appearances on the network.

NBC insisted it acted responsibly. But the network and its rivals, ABC, CBS and Fox, said they would limit future use.

"Once you've seen it, its repetition is little more than pornography once that first news cycle is passed," said Jeffrey Schneider, ABC News senior vice president.

The package received by NBC News on Wednesday carried a time stamp showing Cho mailed it after he killed his first two victims in a dormitory but before he went on to slaughter 30 more in classrooms. NBC turned the material over to the FBI.

"That's crazy. He kills two people and then goes to the post office and then he's ready for round two? It's creepy," said graduate student Nick Jeremiah, 34.

The dead included not only Americans but students from Vietnam, Indonesia, India and Egypt. A professor with dual US-Israeli citizenship was also killed, hailed as a hero for barring the door to give students time to escape.

In a sign of exhaustion with the media spotlight, a hand-lettered sign on campus said "Media, stay away."

The university said Cho's victims would be awarded their degrees posthumously. Though classes resume on Monday, students can request an immediate end to their semesters with credit for work already done, Virginia Tech said.

The images and rambling monologue suffused with paranoia added to a chilling portrait of Cho, a 23-year-old student whose dark writings had worried professors and classmates.

NBC News President Steve Capus defended the broadcast of the material, saying: "This is I think as close as we will ever come to being inside of the mind of a killer."

ADMIRATION FOR COLUMBINE KILLERS

Cho is shown railing against wealth and debauchery and voicing admiration for the 1999 Columbine High School massacre. "You have vandalized my heart, raped my soul and tortured my conscience," he says, speaking directly to the camera.

Cho immigrated from South Korea in 1992 and was raised in suburban Washington, where his parents work at a dry cleaners.

Police disclosed on Wednesday that Cho had been accused of stalking women students and was taken to a psychiatric hospital in 2005 because of worries he was suicidal. That has raised questions whether his later actions had been foreshadowed.

Reflecting nationwide security jitters, schools in Yuba City, California, were ordered into a "lock-down" after police warned a man had threatened a killing spree in locals schools.