OSLO (Reuters) - Norway agreed on Wednesday to review security and the police response to the killings of 76 people in bombing and shooting attacks by a right-wing zealot that have traumatised the nation. Jittery Norwegians tried to restore some normality five days after the bloodshed, despite a security alert forcing the evacuation of Oslo station, keeping nerves on edge. Its important to clarify all aspects of the attacks to learn lessons from what has occurred, Prime Minister Jens Stoltenberg said after parliamentary leaders agreed to appoint an independent commission to review the attack. This is a national tragedy, an attack on the nation. Questions have been raised about whether the police acted too slowly when Anders Behring Breivik massacred 68 people on July 22 after setting off a car bomb in Oslo that killed 8 people, and whether security in the Nordic nation is too lax. (Police) organisation and capacity will be part of an evaluation, Stoltenberg said. He expected the attacks to stimulate political engagement among his compatriots, he said. Breivik is said to have given varying accounts of his actions, first saying he operated alone and then telling a judge he was part of a wider network. Norway's domestic intelligence chief said she believed Breivik was a lone operator and contested an assertion by his lawyer that his client was probably insane. So far we have no indication that he has any accomplices or that there are more cells, Janne Kristiansen told Reuters. When we have finished this stage of investigation, we have to sit down, police and security services all over the world, and consider what we can do differently and what we can do to avoid these lone wolves. Oslo's central station was evacuated after a suspicious suitcase was found on a bus. Police said later it was harmless. In another false alarm, police retracted a search alert for a man who they suspected of sympathising with Breivik, saying in fact they wanted to detain a mentally ill man with no link to the killer. A cabinet minister made a symbolic return to her office in Oslos government district where Breivik detonated a powerful home-made bomb that killed eight people on Friday. The bomb blew a hole in Stoltenbergs office. For now, he will work from the defence ministry in a different area of Oslo and cabinet meetings will be held in a medieval fort near the waterfront. It is not clear whether the 17-storey prime ministry building will be rebuilt or torn down. I am glad to be back in my office...to be able to resume the more normal work functions, Administration and Church Minister Rigmor Aaserud told reporters. Her office, in a government complex, was little damaged. In Stoltenbergs building, which took the brunt of the car bomb, curtains still flapped from broken windows. Stoltenberg has won high opinion poll ratings from voters for his handling of the crisis, with about 80 percent of Norwegians reckoning he has performed extremely well, according to a survey published in the daily Verdens Gang. The prime minister, who knew some of the victims, has caught the national mood, urging his compatriots in a voice often cracking with emotion to unite around democratic values. Yes, I have cried, he said of his personal reaction. Norwegians, unused to violence in a quiet country of 4.8 million, must now struggle with how to improve security without jeopardising the freedom and openness of their society. Our challenge will be to reconcile those two things, Stoltenberg said, denying that Norway had been naive. It is very important to distinguish between naivete and openness. He said he welcomed a debate about security measures and the police response to the emergency. Some critics have accused the police of taking too long to reach the island northwest of Oslo where Breivik shot 68 people, mostly youngsters at a summer camp for the ruling Labour Party's youth wing. Police took more than an hour to reach Utoeya and arrest Breivik. He threw down his gun and surrendered when officers approached him, a policeman involved in the arrest said. Stoltenberg said Norway had special forces designed to deal with violent attacks, even if these had not occurred before. We are even more aware of any dangers now than before the attack. But in general Norwegians want ... to defend themselves against violence by showing they are not afraid of violence. CONTROLLED EXPLOSION On Tuesday night police destroyed an explosives cache found at a farm rented by Breivik, some 160 km (100 miles) north of Oslo. They believe he made his bomb using fertiliser which he had bought under the guise of a farmer. They detonated another cache on Wednesday. Breiviks lawyer, Geir Lippestad, said his client was probably mad, but it was too early to say if the loner and computer game enthusiast would plead insanity at his trial. Breivik has confessed to his actions, but denied guilt, saying he was part of a network with two cells in Norway and more abroad that was fighting to save European Christendom from the spread of Islam and multi-culturalism. But police believe Breivik probably acted alone in staging his assaults, which have united Norwegians in revulsion. Breivik, 32, has asked that non-Norwegian psychiatrists assess him, police lawyer Paal-Fredrik Hjort Kraby said. Flowers left by Norwegians to show their grief for Breiviks victims decked Oslo's main thoroughfare, Karl Johans Gate. Police say about 200,000 people, a third of the citys population, turned out for a commemorative rally on Monday. Police reopened some streets around the blast site in Oslo and shops gradually reopened for business. Breivik, who was remanded in custody for eight weeks on Monday, has been charged under the terrorism act, which carries a maximum penalty of 21 years in jail, but the authorities are considering whether to charge him with crimes against humanity. Stoltenberg said that Norway had a system allowing sentences to be extended if there were a risk of new crimes.