Representatives for the state have insisted that the rightwing extremist, who killed 77 people in Norway in 2011, must be kept in isolation because he is dangerous.
"The plaintiff is not, nor has he ever been, subjected to inhuman treatment," argued Adele Matheson Mestad from the office of the general attorney.
Norway's most infamous inmate is serving a maximum 21-year sentence -- which can be extended if he is still considered dangerous -- for killing eight people in a bombing outside a government building in Oslo and then murdering another 69, mostly teenagers, in a rampage at a Labour Youth camp.
He finished off many of his young victims with a bullet to the head.
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Since his arrest on the day of the attacks, Breivik has been held apart from other prisoners and his contacts with the outside world, including visits and correspondence, have been strictly controlled.
Stressing his client's almost five years in isolation, Breivik's lawyer Oystein Storrvik accused the state of breaching two clauses of the European Convention on Human Rights prohibiting "inhuman or degrading treatment or punishment" and guaranteeing respect for "correspondence".
As expected, the killer used the four-day proceedings as a platform to grandstand his extremist views.
After making a Hitler-style salute on the first day, he claimed he was now a Nazi who had renounced violence and even compared himself to Nelson Mandela.
Storrvik told the court his client was "in a vulnerable state of mind," a remark to which Breivik, clad in a dark suit and shaven head, did not react.
"This is not a broken man suffering from problems caused by his isolation that we see, this is the same narcissistic, ideologically disturbed" man convicted in 2012, Mestad countered.