Sanity at issue as Breivik trial ends

• NEW: Anders Breivik was motivated by his extreme political views, his lawyer says
• Breivik's trial for the killing of 77 people in July last year is coming to a close
• Prosecutors say they believe he is mentally ill and should be transferred to a mental institution
• Breivik's lawyer says his client wants to be considered sane so people listen to his message

Oslo, Norway (CNN) -- The trial of accused mass killer Anders Breivik on charges of voluntary homicide and committing acts of terror in Norway last summer is due to come to a close Friday.

Breivik has admitted carrying out the July 22 attack on a Labour Party youth camp on Utoya Island that killed 69 people and a bombing in Oslo, targeting government workers, that killed eight.

Breivik, who boasts of being an ultranationalist who killed his victims to fight multiculturalism in Norway, says he acted out of "necessity."

His defense lawyer, Geir Lippestad, is expected to argue in his closing statement Friday that he should be given a full acquittal.

After hearing the closing arguments, the judges' final verdict is due to be delivered either July 20 or, failing that, August 24, court officials said.

The issue of Breivik's sanity is at the heart of the case.

Norwegian prosecutors asked Thursday that Breivik be transferred to a psychiatric institution because they believe he is mentally ill, a spokeswoman for the prosecutor's office told CNN. If that does not happen, prosecutors will ask for 21 years of prison for Breivik.

Giving his closing statement Friday, Lippestad presented his own arguments on the issue of Breivik's sanity, as he sought to argue that his client's past did not point to a history of violent acts.

"The central criterion for insanity is that the ability of realistic assessment of one's relationship to the outside world is largely abolished," he said.

"Is it violent fantasy that is the mother of these actions, or is it his political opinion?"

The lawyer outlined Breivik's political life and activity as heard by the court, from the early days when he was member of a party to the extreme political arguments he posted online.

Lippestad also recalled how Breivik's mother had explained that he at times was extremely interested in politics.

Both she and Breivik's friends said he was intense when he talked about politics, but they never said he was intense about violence, the lawyer said.

Lippestad argued that Breivik had chosen his targets politically, citing how he didn't attack non-political people like the captain on the boat to Utoya, and the youngest children on the island.

The lawyer told the court he shared the prosecutor's view that the attacks, which he called "a cruel act of terrorism," were almost too horrible to be true.

But, he said, the key question for his client was whether he acted under the legal principle of "necessity."

Lippestad has previously said it is important to Breivik that people see him as sane so they don't dismiss his views.

In the course of the trial, which started in mid-April, the court has heard moving testimony from the survivors of the July 22 attacks.

Survivors and relatives of those killed and injured have also been present in the courtroom to hear Breivik give his account of the events of that day and the motivation for his acts.

Last month, Breivik promised that he would not appeal if a court finds him sane and guilty.

In his testimony early in the trial, Breivik claimed to represent a "European resistance movement" and "Europeans who don't want our ethnic rights to be taken away."

The shocking attack prompted Norwegians to reassert their commitment to multi-culturalism and tolerance at a series of mass public tributes.

Journalist Olav Mellingsæter contributed to this report.