The diagnosis was reported on Tuesday in the New York Times, revealing that a group of scientists at New York University had come up with a depravity scale to help explain criminal savagery that defies usual psychological explanation or treatment.
 
While much of the public may think it natural to call vicious serial killers who cannibalise their victims "evil", psychiatrists have always avoided the term since it implies a moral rather than a clinical judgment.
 
But Dr Michael Stone of Columbia University, who has published a 22-level hierarchy of criminal behaviour based on the case studies of more than 500 violent criminals, disagrees.
 
"We are talking about people who commit breathtaking acts, who do so repeatedly, who know what they're doing, and are doing it in peacetime," Stone was quoted as saying.

"We know from experience who these people are, and how they behave," and it is time, he said, to give their behaviour "the proper appellation".
 
List of depravity

Stone's list of evil includes the most notorious serial killers in modern times, such as John Wayne Gacy of Illinois, the killer who strangled more than 30 boys and buried them under his house.
 

"There is a group we call lethal predators, who are psychopathic, sadistic, and sane, and people have said this is approaching a measure of evil, and with good reason"

Robert Hare, professor emeritus, University of British Columbia

His controversial theories are backed by Dr Robert Hare, a professor emeritus at the University of British Columbia in Vancouver who devised a personality test to identify levels of psychopathic behaviour.
 
The 20 items include glibness and superficial charm, grandiose self-worth, pathological lying, proneness to boredom and emotional vacuity, which are assigned numbers according to the response.

Hare found that average scores varied from below five in the general population to the low 20s in prison populations, to a range of 30 to 40 in predatory killers.
 
"There is a group we call lethal predators, who are psychopathic, sadistic, and sane, and people have said this is approaching a measure of evil, and with good reason," Hare was quoted as saying.