"Once you reach a certain level of frustration, people may essentially feel like, 'Forget it, it's not worth trying to achieve what I want by normal, societally acceptable means. I'm going to go out and hurt someone to get what I want.' "

Other studies suggest psychopaths' brains have an enhanced ability to sense certain emotions - in particular, fear.

They seem better able to pick up cues of vulnerability or weakness, making them, in a sense, a natural-born predator.

At this stage, experts can only speculate based on news reports, but several said Magnotta exhibits some of the key characteristics of the "prototypical psychopath." He is also a classic thrill-seeker, says psychologist Dr. Frank Farley, who coined the term "Type T [thrill seeker]" personality.

"I think a lot of killing involves more thrill value than we acknowledge," he said.

But not all are comfortable with the field's sudden rush to the brain. Farley, an Edmonton native and past president of the American Psychological Association, worries a new kind of reductionism is at play. "We're trying to reduce very complex human behaviours to some precise little process in the brain," he says.

It doesn't wash, he says. "Humans have evolved in a complex social world of relationships, families, upbringing and human connections," says Farley, a psychologist at Temple University in Philadelphia. "It can't be boiled down to a microscopic-sized area of the brain," he argues, or one of the thousands of biochemical activities of the brain.

Biology can be a part of it, he says, but it's the social side, "the social influences, the nurturing influences that, in my view, dominate."

For example, abuse in childhood is common among those with psychopathic traits - abuse so relentless, "he has to anesthetize himself against it," says Leyton.

"And in the process of anesthetizing himself, he also loses any touch of his own humanity."

According to Farley, scholars have argued that psychopaths feel deeply about nothing.

Many experts agree that it's not one or the other, nature or nurture, but rather a combination.

"People shouldn't be panicked that there's a cannibal lurking around every corner," says Leyton. "It's just a combination of biological, biochemical, personal psychology and social environment that come together, very rarely, to produce this kind of abomination."

Most psychopaths are not the murderous Hannibal Lecter, said Benning, of Vanderbilt University. They're not even necessarily criminals.

But they do contribute to "a whole lot of heartbreak and ruined lives."

"There are so many societal consequences to individuals who cannot control their behaviour, who are lacking in empathy and who are aggressive toward others," he says.

They are utterly charming, he adds. And you can't see them coming.