What turned Anders Breivik into Norway's worst nightmare?

His face stares out from front pages on news stands all over Oslo and it wears an expression of triumph bordering on glee. Yet nearly a week after Norway's worst act of violence since the Second World War, the mass murderer Anders Breivik has assumed the proportions of an unspeakable monster. He is someone few people want to see, let alone mention by name.

A yellow placard among a carpet of roses commemorating the dead outside the capital's Storting parliament reads: "Putting this man away for 21 years is not enough! We call on all politicians to make him pay dearly for what he has done. Somebody who took all these lives deserves to be put away forever." The placard is unsigned.

Anders Behring Breivik, the 32-year-old one-time farmer who massacred 76, predominantly young, Norwegians in last Friday's Oslo bomb blast and subsequent Utoya island shooting, is not named on the placard. His name was not spoken either during a poignant rally attended by some 250,000 people in the centre of Oslo on Monday night to show sympathy with the families of the dead. Speakers referred to him only as "the perpetrator".

Breivik is someone Norwegians would like to see forever banished. In response to demands that he be locked away for life, state prosecutors are considering charging him with crimes against humanity, rather than mere terrorism, an offence which carries a sentence of 30 years. Breivik's father's answer to his son's crimes are that "it would be better if he committed suicide" and he has refused ever to see him again.

While Geir Lippestad, Breivik's lawyer who specialises in far-right crime, concludes that his client is probably "insane", the response of Jens Stoltenberg, Norway's suddenly massively popular Labour Party prime minister, to Breivik's murder spree has been unwavering defiance. "We are a small country," he declared in an emotional speech after the massacre. "But we are a proud people and we will stand by what we have. Our response is more democracy, more openness and more humanity."

Six days after Norway's horrific shooting and bombing, the overriding impression is of a nation still so shell-shocked by what happened that it has gone into denial. Few, if anyone, have been prepared to acknowledge that Breivik is Norwegian. On paper at least, he is also a product of Norway's middle-class, consensus-bound society which champions the liberal values of tolerance advocated by Mr Stoltenberg. But to the utter shock of Norway, Breivik chose to bite the hand that fed him with a severity hitherto deemed inconceivable. What went wrong? Norway, it seems, is not yet ready to answer the question.

As Mikal Hem, a political columnist for Norway's Dagbladet newspaper, told The Independent yesterday: "A lot of people don't want Breivik to be given any recognition at all. Norwegians are acutely aware that he wants attention and there is a sense that people will not give him what he wants."

However he added: "But at some point we are going to have to ask ourselves some difficult questions about how this man evolved to be the person he became and if we don't ask these questions we will be doing something seriously wrong. Breivik, it has to be remembered, was a man given every advantage by Norway."

A brief drive through the western Oslo district of Skøyen provides an impression of the kind of advantages Breivik was afforded. It is a suburb whose houses have big, green gardens. Unlike Oslo's run-down eastern immigrant quarter, western Skøyen is inhabited by Breivik's successful former schoolmates: doctors, lawyers and management consultants.

Breivik went to school in the district, growing up in a modern housing estate popular with young professional parents. He returned there earlier this year to live with his ailing mother to save money and have "sufficient means and time", as he put it in his 1,516-page "manifesto", to prepare for the act of mass murder he referred to as his "mission".

Next to the bell at house number 18 is a plaque bearing the words "A Breivik. Geofarm" which refers to the farmstead he bought and finally used to manufacture the devastating fertiliser bomb that last Friday exploded in Oslo's parliamentary district.

He seems to have enjoyed a normal Norwegian childhood. "He was an alert but unremarkable boy at school," remembers a former classmate, who wished to be anonymous. "He was somebody who went along with the others. He wasn't an outsider and he didn't appear to have problems."

After school, Breivik did a brief stint in the army, and then appears to have gone from one job to the next. He is believed to have started a computer company and earned enough money to live in a luxury apartment and sport a Breitling watch. However, other reports suggest that for years he worked in a lowly call centre and lived almost anonymously.

He appears to have attracted attention as a 15-year-old when he joined a graffiti-spraying gang and subsequently clashed with an immigrant gang of Pakistani youths whose violence frightened him. When in the army, he joined the youth organisation of Norway's right-wing Progress Party and remained a member for 10 years before finally resigning because he felt the organisation was too much part of the establishment.

Exactly what he lived on in the run- up to the massacre remains a mystery. But his bank details reveal that in 2007, a sum equivalent to €80,000 (£70,000) was added to his account, which would have enabled him to live without having to work.

None of these details provide an explanation for Breivik's decision to gun down 68 youth members of the Norwegian Labour party on Utoya island, convinced their support for multicultural values was encouraging "Muslim world domination".

However, his personal and sexual life may well provide criminal psychiatrists with evidence to explain his warped personality, his clinically obsessive character and even the motive for his acts. One clue is likely to be his ailing mother: she has not spoken or been interviewed since the massacre took place. But if the closing pages of Breivik's manifesto are credible then her ailment appears to stem from the final stages of an unspecified venereal disease which he claims she contracted several years ago and has since reduced her mental state "to that of a 10-year-old".

Breivik appears never to have had a girlfriend worth mentioning. He was born in February 1979, the son of Jens Breivik, a career diplomat and Wenche Breivik, a nurse. Both were Norwegian Labour Party supporters. They divorced when Breivik was only one year old and he lived thereafter with his mother, who worked at Norway's embassies in Paris and London. He only maintained sporadic contact with his father and that came to an end when Breivik was 15.

Neighbours described Wenche as elderly and frail, but added that she was a gregarious and welcoming woman who often chatted to strangers and was fascinated by foreigners. She remarried a Norwegian army major. But although apparently regarding his stepfather as a "good bloke", Breivik appears to have secretly detested him for being a product of permissive Norwegian attitudes to sex. He blames his stepfather for having infected his mother with venereal disease which was also passed on to one of his half-sisters.

"My mother and my sister not only shamed me, but themselves and our family," Breivik writes in his bizarre manifesto confessions. "It is a family that was already destroyed as a result of the feminist/sexual revolution."

He concludes that Norwegian liberalism and permissiveness allowed him "too much freedom" and had "to a certain extent made me feminine". Some analysts outside Norway have already started to advance the theory that Breivik had deep feelings of sexual inadequacy. They argue that he subconsciously sought compensation through gross acts of violence carried out with the help of an assortment of obviously "phallic" weapons such as the automatic rifles, shot-guns and special Glock automatic pistol with which he calmly gunned down teenaged Labour Party members as if they were rabbits.

Breivik took nine years to work out his plans for mass murder. He is even reputed to have bought several bottles of French 1979 vintage wine which he opened each New Year and drank with his family to celebrate the approach of a mission, whose real purpose was never explained. Despite railing against his family's sexual immorality, he claims to have saved up €2,000 to spend on a "high-class" prostitute for the week before his massacre.

When it came to the day, Breivik took innocent, tolerant Norway completely and horrifically by surprise. He hired a Volkswagen van which he had loaded with his fertiliser bomb, drove it to Oslo's parliament, parked it nearby and set the detonator on a timed switch which would cause the device to explode more than one hour later.

He then hailed a silver-coloured taxi which drove him, by now dressed in a stolen police uniform, and his assortment of weapons to Utoya island where 600 adolescent members of the Norwegian Labour party were enjoying a summer camp for the nation's "most promising future politicians".

The taxi driver recalled this week: "There was nothing suspicious about him at all. He seemed just like any easy-going cop. He told me he was just going to check the security on the island because of the bomb blast in Oslo that we were hearing about on the car radio."

The taxi driver hailed the Utoya island ferry boat to come and pick Breivik up. The ferryman willingly obliged. Breivik, with an automatic rifle slung over his arm in a case, was also carrying a large black plastic suitcase full of his other weapons. The ferryman remembers lugging the case up the jetty. "I was a bit surprised how heavy it was," he said in an interview yesterday. Once off the jetty, Breivik unpacked his weapons and like a murderous Pied Piper, began summoning the band of happy campers to come towards him. "I have come to protect you," he insisted as he opened fire.

In the end it was not Norway's immigrants or Muslims that Breivik chose to assassinate, but people who came from the same background as he did and whose parents were almost certainly Labour Party supporters like his own. But the fact was that by last Friday, Breivik felt not only that he no longer belonged to his own people, he had come to detest them with a virulence that was unprecedented.Is Norway's ostensibly tolerant social model partially to blame? Critics point out that in the aftermath of the humiliation inflicted on the country by the Nazi invasion and the imposition of a fascist puppet government during the Second World War, Norway has religiously adhered to an almost stifling form of consensus politics in which the main parties tend to agree on everything.

The upshot is a generous welfare state, excellent schooling, high wages, high taxes and prices and considerable social uniformity. Immigration, which has hit the 20 per cent mark in Oslo and is largely confined to the city's eastern districts, may be high by Norwegian standards but is insignificant when compared to areas in Britain or other parts of continental Europe.

Political commentators like Norway's Kjetil Kollsrud say that consensus politics conducted Norwegian-style have resulted in a form of extreme egalitarianism. "The fact is that in a system like this there is simply not a great deal of room for people who don't fit it," he told The Independent. Anders Breivik was clearly one of those who didn't.