Last week, a Saint Jerome boy, who coolly described how he beat a classmate to death with a baseball bat, was described by psychiatric experts as not responsible because he suffers from a paranoid delusionary disorder. And in another Canadian courtroom, an accused sex-killer was portrayed as a case of multiple personality disorder. While prosecutors and the occasional skeptic may express disbelief, the courts have become so accustomed to listening to psychiatrists explain away hideous crimes, these arguments often sway judges and juries.

When Rita Graveline shot her husband in the back while he slept, psychiatrists testified she was the victim of "battered wife syndrome" which had caused a momentary loss of consciousness or "dissociative amnesia." When Andrew Leyshon-Hughes thrust a carving knife 21 times into sleeping Nancy Eaton and then raped her dying body, psychiatrists rooted back through his history, found that he was a "blue baby" and declared the cause to be his "crocodile brain."

Psychiatry has a long and winding history of describing criminal behaviour in pseudo-medical terms. Since well before the 1978 "Twinkie" defense rationalized two cold-blooded murders as temporary insanity due to the effects of eating too much sugar, we've been swallowing this junk.

These days, there are very few cases in which psychiatrists don't try to shift the focus from the facts of the crime to the mind of the criminal. They were hard pressed to fit a label to Paul Bernardo. And they had trouble finding anything to say about Harold Shipman, the British physician who murdered more than 150 patients. Some crimes, it seems, do still defy explanation.

This situation, however, is about to change. At last month's annual meeting of the American Psychiatric Association in New Orleans, Michael Welner, a clinical associate professor of psychiatry at New York University School of Medicine, proposed that the time has come for psychiatrists to assume responsibility to detect evil. This would be an about-face for a profession that has, for more than two centuries, been telling the courts that vile and brutal acts are symptoms of mental diseases.

It wasn't long ago that psychologist Judith Becker, president of the Association for the Treatment of Sexual Abusers, stretched our imagination when she diagnosed the mass-murderer Jeffrey Dahlmer as suffering from "cannibalistic compulsions." She even went so far as to suggest his problems might "have been alleviated had he felt safe to seek help when his deviant fantasies began in adolescence."

But Welner isn't interested in finding a cure. Instead of offering to help the accused, he intends to help society uncover the evil in our midst. Relying on language of a bygone moral era, he would prefer to consider those like Dahlmer so depraved and evil as to be beyond help -- and beyond mercy. And he is offering his expertise not only to criminal courts but also to family, civil, human rights and military courts. He is prepared to expose "evil acts of evil parents" and the wickedness in employees that causes disputes and disruptions in the workplace. To lend an air of scientific credibility to these value judgments, he has created a "Depravity Scale," a measure that he claims will identify "evil behaviours for the courts."

From time to time other psychiatrists, such as Scott Peck, have talked about evil, but Welner is the first to make a serious effort to sell the skill of detecting it. And what makes his initiative particularly frightening is that he is doing so at a time when the soil is ripe. Crime victims are outraged when the punishment seems not to fit the crime. Words like "monster" are being used to describe hunted criminals and society is caught up in a fearful urge to rid itself of violence.

I can understand the desire to distinguish Good and Evil. And I think that long ago we should have cast aside the foolish notion that evil acts are a sign of sickness. But I am not willing to entrust the profession that brought us the Twinkie defence and "crocodile brain" to tell us who is "evil." I imagine, with dread, how far they might take this power.

Until now, psychiatrists have remained within the bounds of their medical profession. Whether we have believed them or not, they have interpreted criminal behaviour in terms of health and disease. Sometimes the illnesses, such as multiple personality disorder or temporary insanity, were considered curable. At other times, when diagnoses such as psychopathy and pedophilia were used, the conditions were deemed less amenable to treatment. However, whatever they did, like it or not, they stayed within the domain of medicine.

In identifying evil, they are crossing the line into the practice of religion, for "evil" is not an illness but rather a moral state. Determining who is evil is a religious, not a medical, act. By performing it, psychiatrists will become the inquisitors of the 21st century.

In Europe during the 15th and 16th centuries, and later in North America, inquisitors traveled the country hunting out evil using the Malleus Maleficarum, the famous manual for witch-hunters, as their guide. Serving as the expert witnesses at the witch trials, they distinguished diseases due to natural causes from those caused by demons.

If Welner's idea takes hold, these inquisitors could rise again, disguised as psychiatrists and using the Depravity Scale as their guide.