Defence lawyers on Friday asked that Anders Behring Breivik be acquitted or be found sane and sent to prison as the trial of the man who killed 77 people in Norway last year wrapped up.

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Breivik's main lawyer Geir Lippestad concluded two hours of closing arguments on the last day of the trial calling for Breivik to receive "the mildest possible" punishment.

Though there is no chance Breivik will be set free, the defence lawyer was formally obliged to request acquittal since Breivik has pleaded not guilty, despite confessing to carrying out the murderous twin attacks on July 22.

That day, Breivik first set off a car bomb outside government buildings in Oslo, killing eight people, before travelling to Utøya island, north-west of the capital. There, he spent more than an hour methodically shooting and killing another 69 people, mostly teenagers.

The victims, the youngest of whom had just celebrated her 14th birthday, had been attending a summer camp hosted by the governing Labour Party's youth organisation.

Breivik has evoked the "principle of necessity", claiming his attacks were "cruel but necessary" to protect Norway against a "Muslim invasion".

Yet after spending two hours mainly detailing why his client was sane and should be sent to prison and not a closed psychiatric ward as requested by prosecutors, Lippestad appeared reluctant to ask for acquittal.

He fumbled as he wrapped up his arguments, saying just that the defence wanted "Anders Behring Breivik to be viewed in the mildest possible way."

When lead judge Wenche Arntzen asked whether this meant he wanted to request acquittal, he first said "no", but after Breivik himself spoke up saying he had no choice, he conceded: "It is acquittal. That is right."

With no illusion of getting his client off, the defence however mainly focused on the tricky question of Breivik's sanity, which has been the main focus of his 10-week trial, which began on April 16th.

Psychiatric evaluations of Breivik's mental health have sharply contradicted each other, with two court-appointed expert teams reaching diametrically opposed conclusions.

Breivik himself is intent on proving his sanity to establish that his far-right, Islamophobic ideology is not just the rantings of a lunatic.

If found sane when the judges hand down their verdict on July 20th or August 24th, Breivik will likely be sentenced to Norway's harshest penalty: 21 years in prison, with the possibility to extend the sentence for as long as he is considered a danger to society.