The man accused over a bombing and shooting spree that left 77 people dead in Norway has acknowledged carrying out the killings but pleaded "not guilty” on terror charges, as his trial got under way in Oslo."I acknowledge the acts, but not criminal guilt,” Anders Behring Breivik told the court on Monday morning, referring to the July 2011 attacks over which prosecutors accuse him of committing acts of terror.Breivik arrived in court for the morning’s opening session in Oslo amid tight security and massive media attention, with proceedings set to focus on whether or not he is legally sane. Jo Stigen, a law professor at the University of Oslo, told Al Jazeera the trial was a "fascinating case” but added that it was a peculiar situation where the accused claims responsibility for the killings and "now pleads he commited them in self-defence”."To me it sounds a pretty absurd argument,” said Stigen. "If he is declared insane his mission totally will fall apart. So it is extremely important to be considered insane and to be held criminally responsible.”If convicted, the 33-year-old faces a 21-year sentence that could be extended indefinitely if he is still considered a threat to society. If deemed to be insane he would face closed psychiatric care, possibly for life.Upon his entrance to the court, Breivik lifted his right fist in an apparent far-right salute."I do not recognise the Norwegian courts. You have received your mandate from political parties which support multiculturalism”, Breivik told the court, adding that he wished to be tried in a military court. "I do not acknowledge the authority of the court.”Wenche Elizabeth Arntzen, the lead judge responded, telling Breivik that he would have time to make statements later on in the trial. Breivik diplayed little emotion as the prosecutor read out a list of those killed and how they had died as well as his charges, but later appeared tearful as the court was shown a 12-minute film that he had posted online on the day of the attacks.