OSLO - The man who killed 77 people last summer to protest Muslim immigration to Europe said on Monday he believed he could tell the ideology of his prospective massacre victims by looking at them, and tried to spare one who appeared "right-wing"."Certain people look more leftist than others," Anders Behring Breivik said on the sixth day of a trial that has transfixed Norway, explaining how he picked off "Marxists" with his rifle and pistol while passing over a young man he thought looked conservative.Breivik apologetic for first timeBut on Monday Breivik issued his first seeming apology, to innocent bystanders hurt or killed when his 950-kilogram fertilizer bomb went off in Oslo. More than 200 were injured."To all of those ... I want to say I am deeply sorry for what happened," he said. "But what happened, happened."He called his acts "a minor barbarity to prevent a larger one", apparently referring to Europe's supposed cultural decline.The 22-year-old he chose not to kill, a Labor Party youth wing activist named Adrian Pracon, has told Reuters:"I remember him pointing the gun at me for quite a long time before he took it down, turned and walked away."Later in the rampage, which lasted more than an hour, Breivik came upon Pracon again as he played dead, and this time shot the son of Polish immigrants through the shoulder.In another separate apparent bid to show he has a conscience, Breivik pointed out that he spared the life of a 10-year-old boy whom he had had in his rifle sights on the island."I could not understand what such a little boy was doing at a political indoctrination camp," said Breivik, whose victims were as young as 14.The boy's name has not been released by the authorities but his father, Trond Berntsen, was an off-duty police officer serving as the island's security guard. He was Breivik's first victim, according to the indictment.Ahead of the trial, which is expected to last 10 weeks, one court-appointed team of psychiatrists concluded Breivik was psychotic while a second found him mentally capable.If Breivik is deemed sane, as he hopes to be, he could face a 21-year prison sentence with indefinite extensions for as long as he is considered dangerous."This person ... appeared right-wing, that was his appearance. That's the reason I didn't fire any shots at him," said Breivik, 33, whose sanity or lack of it is a prime issue to be determined in the trial.Breivik has given a detailed account of his car bomb attack at government headquarters in Oslo, which killed eight people, and a follow-up gun massacre at a Labour Party island camp where he killed 69, mostly teenagers, all within a few hours on July 22.Most Norwegians have reacted with contained horror to the content of Breivik's testimony, delivered in a cold, matter-of-fact manner, while there is wide public acceptance of his right as a defendant to give it.Breivik has had almost free rein to issue warnings against immigration and explain how he scoured the Internet for bomb-making recipes while writing a 1,500-page document declaring himself part of a secretive group that is Europe's answer to al-Qaida - a group the police have said likely does not exist.Breivik has denied criminal guilt, insisting that his victims were "traitors" whose multiculturalist views facilitated what he saw as a de facto Muslim invasion of Europe.