In 2011, Anders Breivik murdered 69 teenagers in a socialist summer camp outside the Norwegian capital of Oslo, and eight adults with a bomb attack. His hatred was directed at the children of Norwegian politicians who had allowed immigration to contaminate the sturdy bond (as he saw it) of Nordic race and nationhood. ‘You will all die today, Marxists!’ he hurrahed as he stalked and shot his way to infamy.

Inflated with self-importance, Breivik was a self-styled ‘Justicious Knight Commander’ come to cauterise Norway of bloody foreigners. He advocated the racial rejuvenation of his homeland through the expulsion of Muslims, and to this end he photographed himself in masonic Crusader regalia, sumptuously gold-braided and primed for holy war. Was he mad? In many ways he was a grotesque mirror image of Islamist serial killers like Mohammed (‘Jihadi John’) Emwazi.

Like Emwazi, Anders (‘Holy War’) Breivik despised the culturally mixed-up, mongrel Europe in which many of us now happily live, and called for a nation state cleansed of feminists, homosexuals, Jews and bleeding hearts of all stripes. According to the Oslo-born journalist Åsne Seierstad, Breivik was a compulsive computer-gamer. The shooting game Call of Duty had, he thought, improved his firing accuracy no end: the world would have to take Anders the Crusader very seriously indeed.

Why grant Breivik more publicity? He is now almost as famous as his compatriot Henrik Ibsen. In recounting the life and times of this wretched inadequate, Seierstad risks providing a platform for his mono-mania. Better let him fade into insignificance. Yet her point is well made: Breivik was one who preferred to be noticed and infamous rather than not noticed at all, and to that extent he was very much a product of 21st-century celebrity culture. There will be more like him.

Seierstad, best known for her non-fiction reportage in The Bookseller of Kabul, has chronicled Breivik and his twisted ideology with immense narrative verve and psychological acuity. Drawing on trial transcripts, police reports and interviews with survivors, she describes a deepening social malaise in Norway and one man’s wish to undermine its social-democratic experiment in a burst of bloodshed.

Born in 1979 in middle-class Oslo, Breivik was a diplomat’s son who nurtured a corrosive sense of social grievance. His parents had divorced when he was a toddler and his mother was left ignominiously dependent on child welfare. Breivik grew up into a narcissistic, mother-bound teenager, who applied makeup to his pasty face and sought plastic surgery for the bump in his nose (which, he believed, made him ‘look like an Arab’). He had no girlfriends that anyone knew of; people suspected he was gay.

In the early 1990s he got into hip-hop music and became Oslo’s self-vaunted top ‘tagger’, spray-gunning graffiti onto railway sidings and trains. His best mate at this time, interestingly, was a Pakistani, whose street slang Breivik mocked humorously enough as ‘Kebab Norwegian’. There was no sign yet of any dilettante expression of Norwegian fascism, though Breivik did briefly join the xenophobic Progress Party, a sort of Scandinavian Ukip with Viking knobs on.

After setting up an online business selling false university diplomas, Breivik became obsessed by the ‘Muslim threat’ to western civilisation. It is not clear how or why this occurred, says Seierstad. From deranged, off-piste internet sites, however, he learned that shadowy medieval cabals and conventicles such as the Mystical Legates of St Paul and the Knights Templar had taken up cudgels against Islam; he would have to do the same before it was too late.

In a remote farmhouse north of Oslo he began to stockpile bags of explosive fertiliser, telescopic rifle sights, protective clothing, a variety of ordnance and quantities of Red Bull energy drink (he would need all his strength on the day of reckoning). On 22 July 2011, disguised as a policeman, the whey-faced 32-year-old Crusader drove to Oslo’s government district, where he detonated a powerful homemade car-bomb. Minutes later, armed with an assault rifle, he made his way to the summer camp on Utøya island. He had a good hour’s worth of killing there before he surrendered to the police. At his trial the spree killer was judged not to be mad and sentenced to 21 years in jail; he expressed no remorse at all for the young lives he had extinguished, but vowed to continue his good work behind bars.