LONDON - Anders Behring Breivik, the Norwegian on trial for the mass murder of 77 people last July, has puzzled mental health experts trying to decide one of the central questions in the case: whether he is sane or in touch with reality.

Breivik, who pleaded not guilty but admitted the killings, has said being labeled insane would be a fate worse than death, though his lawyer initially did just that.  

Norwegian anti-Muslim fanatic Anders Behring Breivik attends his trial in a courtroom in Oslo April 24, 2012. [Photo/Agencies]

So confusing is his case that two teams of court appointed psychiatrists reached vastly different conclusions about his mental state: one team found him psychotic while another said he was mentally capable.

"You expect with psychiatric disorders to see a level of distress and incoherence," said Roderick Orner, a Norwegian psychologist who specialises in traumatic stress and a visiting professor at the University of Lincoln.  

"We don't see that in Breivik. He falls into this extraordinary category of people - he's not insane, he's not psychiatrically ill, he's a man with a very personal mission."

With unnerving calm and a burning gaze, Breivik related at his trial in Oslo how he systematically planned, prepared and then carried out the killings.

He said he was a nice person who only picked victims with a "leftist" look, sparing one who appeared "right-wing" and several others who were too young.

At one point Breivik said he called police to surrender, only to find himself forced to leave a message.

"He is in no way deluded about what he has done," said Orner, who was in Oslo on the day of the attacks, when Breivik detonated a car bomb in central Oslo before running amok on a small island, hunting down and shooting dead 69 people.

What makes Breivik's case particularly interesting to psychologists is that in other mass killings, the executor typically commits suicide or is killed by police.

"They've got here somebody who's done all that and he's still here to be interviewed and held to account in court," said Ged Bailes, a UK-based consultant forensic clinical psychologist.

If found guilty and sane, Breivik faces a maximum 21-year sentence but could be held indefinitely if he is considered a continuing danger. If declared insane he would go to a psychiatric institution indefinitely with periodic reviews.

World of computers

Breivik, who spent years playing World of Warcraft and Modern Warfare computer games, said he had to force himself to "dehumanize" those whom he felt were his "valid targets".  

"I have not detected any clear signs of psychosis but the issue is whether he has delusions and delusions are difficult to track," said Paal Groendahl, a forensic psychologist in Oslo.

"It depends on how your personality is before you go into this world of computer games, some vulnerable person will have difficulty separating reality from fantasy."

Some psychologists say his behaviour and statements fit the definition of a sane person with a personality disorder.

People with anti-social or dissocial disorders include callous unconcern for the feelings of others, a low tolerance for frustration, incapacity to experience guilt, and a tendency to blame others, traits displayed by Breivik.

"You only need to look at that and you can see Breivik has a dissocial or antisocial personality disorder," said Michael Reddy, an associate fellow with the British Psychological Society who specialises in pathological behaviours within organisations.

"He doesn't have a general inability to understand the world. He understands it very well. He even understands that his particular closed-in world view is in conflict with conventional reality."

Breivik's view is that the forces of immigration were a great danger to the Norwegian people.

"He's clever, effective. He's sane in that he knows what he has to do, but he is heartless in what he has done," said James Thompson, a senior honorary lecturer in psychology at University College London.

Breivik, a former business fraudster who lived with his mother, argued that Muslim immigrants were overrunning Norway. He surrendered as commander of the Knights Templar resistance, a group prosecutors say does not exist.

The distinction between mad or bad individuals is not necessarily clear-cut, specialists say.  

"It's a hell of a complex case," Bailes said. "Mad people can do bad things and bad people can become mad. There are lots of areas of overlap."