Dr. Elliott Leyton is probably the world's most widely consulted expert on serial homicide. The anthropology professor from Memorial University of Newfoundland has made a career of studying why some murderers can't stop killing.

He's written 11 books during his career but his most famous is probably Hunting Humans, an examination of the world's most notorious serial killers that was first published in 1986.

The book has been translated several times and has become required reading for many homicide detectives. It's also found fans in anyone else who is fascinated by serial killers.

Leyton recently revised and updated the classic for a new edition, delving further into what motivates multiple murderers and what kind of cultures provide the breeding conditions of a killer.

"I spent 20 years teaching the subject and thinking about it and reading the research done by people who had followed me into the field. I had a lot of chance to rethink and get all kinds of new information, new data, new diaries of killers, new everything," he told CTV's Canada AM from St. John's.

"So when I was approached by my publishers in Spain, the United States and Canada to do a completely new, updated, revised edition, allowing me to express all the changes in my thinking, I just leapt at it."

Leyton says he rethought many of his theories on what makes a serial killer tick and revised many of them in the book.

"I think when I was writing that book, I was a raging young man raised in the 20th century scientific tradition of "my way or the highway". That's the way scientists think: it's my profession, my discipline knows everything and you don't know anything. So the original book was a very narrow, unilateral view of an anthropological study of people.

"But I've learned a lot over the last 20 years and I've come to have a much more balanced approach since then. And so I've tried to integrate insights from biology, biochemistry and psychology, as well as my own discipline."

Leyton says what he's discovered about serial killers is that they are all in some way disenfranchised. They are social outcasts whose ambitions haven't been fulfilled.

And they blame their failure on a particular group that they feel is responsible for denying them their proper place in society. They begin fantasizing about a campaign of vengeance against the group.

Many sociologists have noticed a gradual increase in the number of serial killers over the past century. Leyton believes that has a lot to do with urbanization, and a loss of "community", along with cultures that glorify violence.

He notes though that even if those problems are eliminated, there are always going to be serial killers.

"Wherever you go, one per cent of murders are serial murders. So if you have a very high rate of homicide, as they do in the U.S. or Russia, you're going to have very high number of serial killings."

Excerpt of Hunting Humans: The Rise of the Modern Multiple Murderer

The D.C. Snipers

"I like killing people because it is so much fun."
. . . attributed to Lee Boyd Malvo

The world was riveted by their murder spree in October 2002, in the course of which they shot and killed ten people and wounded three more in the Washington, D.C., area alone. They seemed to be invisible and appeared out of nowhere, then killed and disappeared as if by magic. All the experts had been flummoxed, mystified by the killers' identities and motives: Few had guessed there were two snipers, and fewer still had thought they might be anything other than the usual angry white males. Yet the dominant male suspect in the killing team was a raging African-American from the slums of Baton Rouge, a decorated veteran from the Gulf War who had converted to Islam; and his enthusiastic accomplice was allegedly an insecure West Indian boy desperate for a father.

They seem to have thought of themselves as heroic rebels striking a blow against the oppressive and racist white state, and there seemed a certain logic in the spawn of the slums of Baton Rouge and Kingston striking at the heart of middle-class America. Lofty yet entirely bogus political motives are a common self-serving justification among these remorseless killers who—just like the savage Columbine school killers—prey on the innocent while venting their anger and indulging their own exalted sense of superiority. Similar illusions accompanied black activist Mark Essex when he shot a honeymooning couple as an alleged blow against the racist state; when DeSalvo killed "to put something over on high class people"; when Starkweather murdered to erase his position at what he thought was the bottom of society, collecting other people's garbage; and when both Bundy and Kemper killed young women students to get even with the upper class and its "brats" and to make their "little social statement." But the fact of the matter appears to be that they were merely acting out their rage as part of a clumsily designed terrorist campaign to extort ten million dollars from the American taxpayer.

If Muhammad and Malvo were an unlikely pair, their motives seemed more focused. There had been some 500 sniper attacks in the U.S. between 1976 and 2000, and the motives for them had typically seemed vague, even trivial. Thomas Dillon, for example, killed five hunters and fishermen in Ohio between 1989 and 1992, his only apparent motive an adolescent fantasy in which he would escape from his dull life as a draftsman for the water department in Canton, Ohio, to fulfill a dream he had had since high school—to kill someone. Personal and sub¬political protests, often over minor provocations and slights, are not just confined to the juvenile murderers who terrorized Colum¬bine High School.

The D.C. Snipers seemed indifferent to the race of their victims, but most serial killers (like most killers in general) prey upon their own race, like Wayne Williams, the black disc jockey in Atlanta who murdered black children, or Ted Bundy, who murdered white women. Although Malvo seems to have been abandoned by his parents for much of his life, the role of child abuse in the creation of serial killers remains unclear: Many killers have relatively normal childhoods, and many who were abused as children go on to lead normal lives. Regardless, most criminologists would agree that a sexualized lust for revenge, power, and control is the most common motive for serial killings; although criminologist Eric Hickey thought the snipers' killings were also a kind of communiqué to American society: "It wasn't the process of killing so much, it was about eliciting a response from the ¬community."

In fact, the D.C. Snipers appear to have been motivated by a vague hostility toward America and a strong desire for extortion. Investigators believe that the motive for the shootings was a bizarre plan to terrorize the region in order to intimidate the government into giving them $10 million to stop the shootings. Whatever their motives, they began shooting long before they arrived in Washington, D.C.: In all, they would be suspects in twenty-one shootings, including thirteen deaths, in Alabama, Georgia, Louisiana, Maryland, Virginia, Washington state, and the District of Columbia.

From Hunting Humans: The Rise of the Modern Multiple Murderer by Elliott Leyton, to be published by McClelland & Stewart Ltd. on August 13, 2005. Reprinted with permission from the publisher.