In 1941, American psychiatrist Hervey Cleckley published a seminal book about psychopaths called The Mask of Sanity, in which he described an intelligent and cunning person skilled at manipulating others and indifferent to their pain. A man like this, Dr. Cleckley explained, finds no real meaning in love or horror or humour, as if "colour blind" to human feeling.
Succeeding on his superficial charm and purity of focus, he walks the paces of a normal person, yet carries "disaster lightly in each hand." A man like this can wear the uniform of social responsibility, even pilot planes for the Queen of England, and be quite a different beast inside.
These traits come remarkably close to describing the horror of Russell Williams.
"I don't know the answers," the former Air Force commander said in his confession, when asked if he'd reflected on his crimes. "And I am pretty sure the answers don't matter."
Society would beg to differ. Since his arrest, we've been wondering: How did he get away with it? Most of those grim details we now know. But science is closing in on the answer to a more compelling question: What made him become the kind of man who would want to?
Dr. Cleckley used interviews, observation and medical records to learn about his patients, but today, brain imaging offers scientists a new way to peer behind the mask. A growing number of them now see psychopathy as a neurodevelopmental disorder, one in which a combination of genetic and environmental factors, such as neglect or poor bonding with parents, lead to deficits in the brain. And if biology is to blame, can society hold the psychopath responsible?
The brain deficits that neuroscientists have documented affect the ability of psychopaths to feel emotions and learn from their mistakes - as if they have a learning disability that impairs their emotional development, says Kent Kiehl, a neuroscientist at the University of New Mexico. The differences have been seen in the brain images of children as young as 5.
Dr. Kiehl has been amassing the brain scans of convicted criminals, at least 15 per cent of whom are estimated to be psychopaths. He and other researchers are now turning their attention to the study of children, searching for the triggers and types of experience that shape the brain of a child or adolescent at risk of becoming a psychopath.
So far he has imaged the brains of 200 young offenders in the American criminal justice system, including many in maximum security, he says. They are assessed for psychopathy using the standard checklist for juveniles, developed by Canadian psychologist Robert Hare and his colleagues.
He is not ready to report his results, but Dr. Kiehl says his hypothesis is that their brains will share many of the same features he has documented in adult psychopaths in U.S. prisons, although the impairment will not be as severe, and thus perhaps more easily corrected.
The brains of psychopaths seem to be stunted in the machinery involved in humanity's ability to feel empathy and kindness, even love. In adult psychopaths, the almond-shaped structure called the amygdala that generates emotions like fear and is also involved in learning, is significantly smaller. They appear to have weaker connections in the inner recesses of the brain that make up the paralimbic system, which involves emotions and self-control. (Psychopathic traits have also been seen in patients with damage to this area.)
There also appear to be differences in the corpus callosum, which joins the right and left hemispheres of the brain - which has been linked to their impressive ability to lie and cheat and manipulate people, an evolutionary advantage in a world that rewards those who get the upper hand, says Yu Gao, a researcher in New York who studies the neurobiology of psychopathy. Think of serial killer Ted Bundy, who sexually assaulted and murdered at least 30 women in the 1970s, and yet earned glowing letters of reference from his boss, the Governor of Washington.