The Norway mass killer will appear in court this afternoon, charged with terrorism.
Anders Behring Breivik wants to tell Norway why he killed at least 93 people, says his lawyer.
Lawyer Geir Lippestad told local media: "He has been politically active and found out himself that he did not succeed with usual political tools and so resorted to violence."
"I await a medical assessment of him.
"He explains himself fairly calmly but every now and then expresses emotion. He buries his head in his hands.
"He has said that he believed the actions were atrocious but that in his head they were necessary."
Breivik, who has asked if he can wear a uniform in court, has admitting carrying out the bomb attack in central Oslo and going on a shooting rampage on the island of Utoya, but he denies any criminal responsibility.
During the hearing, Breivik will not be required to enter a guilty or innocent plea.
Under Norway's liberal laws, a suspect can only be sentenced to a maximum of 21 years in jail. However, this might be extended if courts believe there is a risk of a repeat offence.
Lawyer Mr Lippestad said his client did not think he deserved punishment.