OSLO - Norwegian mass killer Anders Behring Breivik is suffering from development and neuropsychiatric disorders but is not a paranoid schizophrenic, a top expert said on Friday in testimony rejected by the visibly agitated defendant as "insulting".

Breivik, on trial for the murder of 77 people last July, is facing scrutiny over his mental health as the court seeks to determine whether he was sane at the time of his bombing and gun rampage.

One team of experts concluded he was psychotic, suffering from paranoid schizophrenia, while another came to the opposite conclusion, leaving the five judge-panel to decide.

"This is difficult ... but I challenge (the first report) as I find no evidence of paranoid schizophrenia," Ulrik Frederick Malt, a professor at the University of Oslo told the latest hearing in Breivik's ten-week trial.

However, Breivik likely has Asperger syndrome, a pervasive development disorder which often starts in childhood, Tourette syndrome, a neuropsychiatric disorder, narcissistic personality disorder and possibly suffers from delusions, Malt said.

Breivik, who watched much of the testimony with an uncomfortable smile, interrupted, calling Malt's testimony "insulting" and the court procedure which forced him to listen quietly "ridiculous".

Malt said his conclusions are supported by Breivik's loneliness, depression, illusions of grandeur, indifference to others' pain and facial twitches, among a long list of other symptoms.

Once allowed to speak, Breivik lashed out: "I want to congratulate Malt on a well-executed character assassination. In the beginning I was quite offended, but eventually I think it was pretty funny. The premises outlined are not true.

"I'm not an egoist, I'm an altruistic person."

Breivik's childhood psychologist, who recommended removing him from his family at the age of four because of developing disorders, was also expected to testify on Friday but was granted leave due to patient confidentiality considerations.

Several other psychiatrists are expected to testify next week as Breivik attempts to prove he was sane. He called the prospect of being declared insane "worse than death".

Breivik killed eight people on July 22 with a fertilizer bomb at government headquarters, then gunned down 69, mostly teenagers, at the ruling Labor Party's summer camp, shooting victims in the head from close range.

He carried out the attacks claiming to be a commander in the Knights Templar group, an organisation prosecutors say existed only in Breivik's head.

He planned his attacks using computer games, such as Modern Warfare, a first-person shooting game, and once spent an entire year isolated from society, playing games for hours on end.

Breivik said the killings were gruesome but necessary as his victims, the youngest of whom was 14, were traitors who supported Muslim immigration that he said was adulterating pure Norwegian blood and would soon lead to a civil war.

Whatever the eventual ruling, Breivik is likely to spend the rest of his life in Ila prison on the outskirts of Oslo.

If found sane, he faces a 21-year sentence with the possibility of indefinite extensions as long as he is deemed to pose a danger to society. If found insane, he will probably be moved to another area of his prison.

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