Anders Breivik has been found to have been insane at the time of the Norway terror attacks and suffers from paranoid schizophrenia.
Psychiatrists Torgeir Husby and Synne Sorheim compiled the report on Breivik after conducting 13 conversations with the self admitted attacker, also reviewing more than 130 hours of police questioning.
Breivik lived in his "own delusional universe where all his thoughts and acts are guided by his delusions," the 240-page report found.
Public prosecutor Svein Holden said: "They (Husby and Sorheim) conclude that Anders Behring Breivik during a long period of time has developed the mental disorder of paranoid schizophrenia, which has changed him and made him into the person he is today."
"He believes he is chosen to decide who is to live and who is to die," he added. "Breivik stated that he committed these 'executions' out of love for his people. He describes himself as the most perfect knight since the Second World War."
Breivik is set to appear on trial on 16 April though the issued report may affect this planned hearing. The conclusion will also have an influence on Breivik's punishment with long term psychiatric care a possibility over long term incarceration.
The report's findings are not legally binding but hold significance in the upcoming trial.
Breivik admitted to the attacks in Oslo and on Utoya Island on 22 July which claimed 77 lives. He claimed not guilty to the charges after denouncing the Norwegian government for the "mass import of Muslims". He published a 1500 page 'manifesto' just hours before the attack, called "2083: A European Declaration of Independence".
In it Breivik claimed that he was part of a 12-man right-wing group called 'Knights Templar', founded in London in 2002. Norwegian police said that Breivik said he acted alone in the attacks and that his links across Europe were exaggerated.