With mass murderers, the silence is not of the lambs but of the killers themselves.
While serial killers like Ted Bundy slay individuals over an extended span of time until they are caught, mass murderers like George Hennard -- whose 10-minute, 22-victim rampage through Texas cafeteria on Wednesday is the nation's deadliest shooting ever -- kill in a single episode of hyper-violence that usually ends with their own deaths.
As a result, mass murderers take with them vital psychological evidence that criminologists might use to develop a profile of such killers -- much in the way that the FBI has done with serial murderers, a dazzling bit of forensics that formed the basis of the hit movie "Silence of the Lambs" last year.
"[Mass murderers] incubate these fantasies of romantic, vengeful killing sprees; they expect to wreak havoc, make their point and die gloriously," said Elliott Leyton, an anthropologist and author of "Hunting Humans," a book about mass killers. "Serial killers, on the other hand, expect to keep on killing."
Indeed, that is perhaps the biggest difference between serial killers and mass murderers, say psychologists and others who have studied both -- the former enjoy the cat-and-mouse aspect of killing repeatedly over a long period of time, matching wits with police who are trying to catch them, while the latter act in a single, violent episode in which they purge a pent-up rage.
"A serial killer kills for the pleasure of killing; the killing is an end in itself," said Jack Levin, a sociologist and author of "Mass Murder: America's Growing Menace." "With a massacre, it's not fun; it's a means to an end. This is not a game, the way it is for a serial killer. It's a necessity."
Academicians such as Mr. Levin, who teaches at Northeastern University in Boston, tend to agree that mass murderers act in anger over a particular group of people -- be they women, an ethnic group or a group of their co-workers or relatives -- that they believe has wronged them in some way. The drifter Patrick Purdy, for example, apparently targeted Southeast Asian schoolchildren in his January 1989 rampage on a Stockton, Calif., schoolyard; Marc Lepine, the gunman who opened fire on women at a Montreal university in December 1989, harbored a resentment against feminists.
"They feel this group is responsible for denying them their rightful place in society," said Mr. Leyton, a cultural anthropologist who teaches at Memorial University of Newfoundland.
"Most massacres are directed against a particular group, like family members or co-workers," said Mr. Levin, citing R. Gene Simmons of Russellville, Ark., who killed 14 members of the same family in December 1987, and Pat Sherrill, the postal worker who killed 14 people at the Edmond, Okla., post office from which he was about to be fired. "Whether they're trying to kill women or a community, they're getting even. They hold a grudge against these people, and blame them for their problems."
Police speculate that Mr. Hennard might have been gunning for women as well; he had called them "vipers" in a past letter to two female neighbors.
What experts on the criminal mind can't definitively answer, however, is what turns angry persons -- which at some point or another includes all of us -- into killers. "There are probably millions of angry people, and they don't kill," Mr. Levin said. "They go back to sleep, or they change their goals or they get new jobs. Or they don't have the means to weapons of mass destruction."
Mr. Levin said one explanation is a loss of some sort turns internal anger into external action.
"I always look for a personal loss -- a catastrophic one, from the killer's point of view -- such as the loss of a job or a relationship," he said. "It pushes the guy over the edge."
Additionally, the person is usually isolated in some way, without the support from families, friends, church or other groups that the rest of us turn to in times of loss, Mr. Levin said.
What sets such killers off is usually not something that just happened yesterday, a psychologist and former police officer said.
"It's like a pressure cooker, with all this steam that has built up over time," said Harvey Schlossberg, a Forest Hills, N.Y. psychologist and former New York City policeman. "Most of us don't break because we have other outlets; we have families or something. I suspect [Mr. Hennard] had no support system."
Mr. Leyton, the anthropologist, said he believes that there is something in the American character that contributes to the fact that this country produces more serial and mass murderers than any other. He calls it an American male "romance" with violence that pervades all levels of the culture, from the street level on up.