A spokesperson for the prosecutor's office told CNN that if the court hearing the case doesn't agree with the recommendation prosecutors will seek the maximum 21-year prison sentence for Breivik.
Breivik has admitted carrying out an attack at a youth camp on Utoya Island that killed 69 people and a bombing that killed eight people in Oslo on July 22, 2011. Another 242 people were injured.
He boasts of being an ultra-nationalist who killed his victims to fight multiculturalism in Norway.
During final arguments Thursday prosecutor Inga Bejer Engh said how Breivik became a killing machine remains a mystery, the BBC reported.
"We must also accept this court will never find all the answers to our questions," she said.
Final arguments continue Friday with a verdict expected in July or August.
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