As a panel of Norwegian judges mull over conflicting reports on Anders Breivik's mental state during the rampage that killed 77 people in July 2011, a new commentary aims to clarify misconceptions surrounding mental illness and violent crimes.

Breivik, 33, has confessed to a bombing outside the office of the Norwegian Prime Minister in Oslo and a shooting massacre at a Labor Party youth camp on the island of Utoya. More than 500 people were camping on the island when Breivik, dressed as a policeman, began firing.

"When people struggle to comprehend what lies behind the mass murder of adolescents gathered for a weekend of discussions and campfires, the simplest response is that the killer 'must be mad,'" Dr. Simon Wessely, head of psychological medicine at King's College London's Institute of Psychiatry, wrote in the commentary published Thursday in The Lancet. "The inexplicable can only be explained as an act of insanity, which by definition cannot be rationally explained. The act was so monstrous, the consequences so grievous, that the perpetrator had to be insane."

Some experts say Breivik suffered from paranoid schizophrenia, a mental illness marked by delusions. In a 1,500-page manifesto posted online before the attacks, Breivik claimed he was an operative in a violent Christian conservative revolution led by members of the new Knights Templar.

But others argue the attacks, meticulously planned for months in advance, were too organized.

"My colleagues in forensic psychiatry struggle to think of anyone [with paranoid schizophrenia] who has had the foresight to bring along a sign stating 'sewer cleaning in progress' to avoid drawing attention to the smell of sulfur from the homemade explosives in the back of his vehicle," Wessely wrote.

Breivik himself rejected the notion that mental illness fueled his fury, saying the psychiatrists behind the diagnosis lacked "expertise in evaluating violent political activists," the Associated Press reported.

Wessely said Breivik's case also highlights the misconception that people with mental illness get leniency from the courts. In reality, a mental illness defense "may mean that you will spend more - not fewer - years behind bars," he wrote.

If he's found guilty, Breivik faces 21 years or more in prison. If he's found not guilty by reason of insanity, he will be placed in psychiatric care.

"To a political activist, the worst thing that can happen is to end up in a mental hospital," Breivik said in court, according to the AP. "That would delegitimize everything you stand for."