Washington -- Cho Seung-Hui's jarring images and venomous words packaged what one anchorman called a "manifesto" capped a week of terror on the Virginia Tech campus. But as the photos of the 23-year-old shooter-to-be, gun cocked against his head, and his vulgar video commentary saturated the airwaves, they introduced a new danger. Would they prompt more killing rampages?
The answer, say several criminal psychology specialists, is: Possibly, even probably, yes.
"Saturation-level publicity, such as we're seeing with regard to the Virginia Tech case, produces on average two additional mass murders within the two weeks that follow," said Park Dietz, a consultant on criminal behavior who has studied the effects of media coverage on copycat behavior with six crimes, including mass murder, product tampering, and assassination.
Already, fear of copycat attacks has triggered more than a dozen lockdowns at schools from coast to coast in response to a series of new threats that cast in stark relief the daunting responsibility facing security officials in attempting to protect millions of students and employees at schools across the country from acts of mass violence.
Cho's video and voice recordings, played relentlessly on the Internet, also underscored the heightened impact that an individual can have, armed with a video camera and a laptop.
The release of the video met with swift criticism from law enforcement officials as well as Virginia Tech students, who said the images could prove inspirational to other unbalanced individuals.
NBC News officials, which first aired the manifesto material Wednesday night after receiving a FedEx package Cho sent between the two bursts of gunfire, repeatedly explained that they took great care in selecting what to air.
"We felt compelled as journalists" to broadcast it, NBC Nightly News anchorman Brian Williams said Wednesday night, "but I'll tell you we showed restraint."
Still, several experts said that despite an intent to be responsible, the volume and the visceral quality of the coverage is what inspires depressed and paranoid people who have been contemplating a killing rampage of their own to actually go through with it.
"It is something to be concerned about," said Craig Anderson, a psychology professor at Iowa State University, who has studied the impact of several types of media violence. Repetitive news coverage "might give some individuals, who are already predisposed to do something similar, further impetus."
Intense visual coverage of such mass murders can, and often do, serve as a sort of "tipping point" for a small group of people of who identify with the killer, are depressed and paranoid, and had been considering killing out of a sense of revenge and loathing, according to those who have studied it.
Coverage most likely to incite copycat behavior, researchers have found, are emotionally evocative images, biographical details about the killer, and footage of an expansive response - and repetition.
An estimated 9.5 percent of Americans suffer from depression and a significant proportion of Americans are anxious or angry. The proportion of those people who consider murder as a way of taking out their aggressions is small, but all it takes is one or two of those people to be moved by saturation coverage of an effective killer to produce a copycat event.
"The NBC people apparently did the balancing thing and they thought it was more important to get that information across to the public," said Leonard Berkowitz, who has studied copycat murders for more than three decades and is an emeritus professor at the University of Wisconsin at Madison.
"But there is little doubt in my mind that there will be some highly susceptible persons in the mass media audience who will get ideas or say, `Cho was right'," he continued, "and they might act on it."
Several researchers who examine media effects lamented the limited statistics on copycat killings, noting the small sample size and the inability to prove exact cause and effect. But the year 1999 serves as an important test case.
In April 1999, Dylan Klebold and Eric Harris killed 13 people and then themselves at Columbine High School. Eight days later, former student Todd Cameron Smith brought a rifle to W.R. Myers High School in Taber, Alberta, Canada. He shot one student and injured another.
Just three months later, day trader Mark O. Barton, apparently upset over stock losses, killed three family members and then shot up two Atlanta brokerage offices, killing nine and himself, and injuring 13 others. A week later, Alan Eugene Miller shot two co-workers in a Birmingham, Ala., suburb. And workplace shootings followed later in Anaheim, Calif., Honolulu and Seattle.