"We do not see any sign of psychotic symptoms before, during and after" his attacks in central Oslo and a shooting spree on Utøya island near the capital, psychiatrist Agnar Aspaas told the court.
Aspaas and his colleague Terje Tørrissen had been asked to evaluate the right-wing extremists's mental health.
"It is very unlikely that he suffers from an illness in the category of forensic psychiatry," he added.
The evaluation that he was not psychotic at the time of the attacks and can thus be held criminally responsible confirms their psychiatric probe published in early April, days before Breivik's trial opened.
But it is now also based on more than nine weeks of observation during the trial.
An initial probe by official experts Synne Sørheim and Torgeir Husby had found Breivik was suffering from "paranoid schizophrenia", which meant he would most likely be sentenced to psychiatric care instead of prison.
Experts disagree over Breivik's ideological mindset, with some arguing that his "delirious ideas" were symptomatic of schizophrenia and a second group diagnosing a radical minority ideology.
Aspaas and Tørrissen believe that the 33-year-old defendant is an antisocial narcissist, and possibly paranoid. These personality disorders would not keep him out of prison.
On July 22nd, Breivik first set off a car bomb outside government buildings in Oslo, killing eight people, before travelling to Utøya northwest of the capital where he spent more than an hour methodically shooting and killing another 69 people, mostly teenagers.
The victims had been attending a summer camp hosted by the governing Labour Party's youth organisation.
The conclusions of the April psychiatric evaluation, which was ordered by an Oslo court amid an outcry over the initial exam findings, were published just six days before Breivik's trial was set to start.
It will be up to the Oslo court judges to determine Breivik's mental state when they publish their verdict on July 20th or August 24th, thus deciding whether he will be locked up in a closed psychiatric ward or sent to prison.
If found to be legally irresponsible Breivik faces psychiatric internment, possibly for life. If judges on the contrary hold him accountable he risks 21 years in prison, a term that may be extended for as long as he is considered dangerous.
All experts so far agree that the risk that Breivik will continue to be violent is high.
The prosecution is to make its closing statement on Thursday.
"There is no doubt that we are faced with a very difficult situation," prosecutor general Tor-Aksel Busch told NTB news agency.
On Friday, Breivik's lawyers will try in their statements to show that he is responsible for his crimes, in line with their client's wishes, as he fears that his beliefs will be invalidated because seen as pathological.
Breivik claims the attacks were "atrocious but necessary" to protect Norway from multiculturalism and a perceived Muslim invasion. He has admitted to carrying out the attacks but pleads not guilty.