Gunman boasts of killing 77 young people on Utøya, calling it a 'spectacular political attack' and says 'I would do it again'

Tuesday was the day Norwegians hoped they might begin to understand how Anders Behring Breivik became the worst mass murderer in the country's recent history.

Almost nine months after killing 77 people in three brutal hours, Breivik took to the stand at Oslo central criminal court to describe what he called "the most sophisticated and spectacular political attack committed in Europe since the second world war".

Just when it seemed he was taking responsibility for his actions, or showing a hint of remorse, Breivik would deliver a callous endnote. "I know it is gruesome what I have done and I know that I have caused an incredible amount of pain to thousands of people," he said at one point, before adding: "But it was necessary." And: "I would do it again."

In a pre-prepared statement, which the court allowed him to read out for more than an hour – a highly unusual concession granted only because he refused to give evidence at all otherwise – he insisted it was "goodness, not evil" that had prompted him to act in order to prevent a "major civil war".

The persona that emerged during day two of Breivik's 10-week trial was a rambling, repetitive obsessive, fixated on a threat he never truly managed to articulate, but which involved "cultural Marxists", whom he claimed had destroyed Norway by using it as "a dumping ground for the surplus births of the third world".

Norwegians would be a minority in their own capital city within five to 10 years, he said, and he blamed liberal politicians for bringing about Norway's demise by allowing immigration as well as "feminism, quotas … transforming the church, schools".

Often Breivik came across as exactly the kind of "pathetic and mean loser without integrity" that he insisted he was not.

He admitted he had exaggerated the size and reach of the Knights Templar, the shadowy anti-Islamist network he claimed to have joined in London in 2001, because it wouldn't have sounded so impressive to tell of "four sweaty guys in a basement".

You "gild the lily" in order to "maximise the propaganda effect", he said.

He said he regretted creating a "pompous" backstory, and posting pictures of himself wearing a pseudo-uniform cobbled together from eBay, because it had created the impression he was insane.

He repeated over and over again that he knew exactly what he was doing when he planned the attacks.

His targets were not random. The young people he shot dead on the island of Utøya during a Norwegian Labour party summer camp, some of them as young as 14, were "not innocent, non-political children", he said. "These were young people who worked to actively uphold multicultural values. Many had leading positions in leading Labour party youth wings."

The summer camp was like those run by the Hitler Youth, he added.

He told prosecutors he would have preferred to attack a conference of Norwegian journalists, but he had not been able to carry out that "operation".

Some of the survivors were in the courtroom. It was sheer luck that none of Breivik's thousands of bullets hit Tore Sinding Bekkedal, a 26-year-old activist in the Norwegian Youth Labour party (AUF), but Bekkedal said he didn't want the man who murdered so many of his friends to consider him a benign force.

"I don't want him to consider me innocent," said Bekkedal during a break in court. "I want to be a threat to his world model, I really do. I want to be the kind of person that he doesn't consider to be innocent. I want to work for tolerance in society. I think that's a great thing to be working for. There is no enemy I'm more grateful for than Breivik."

During cross-examination, prosecutors tried to tease out exactly when Breivik was radicalised and what the catalyst had been. His answers produced a confusing picture of a teenager who once "had a best friend who was a Muslim".

He said he awoke to the threat of multiculturalism when immersed in Oslo's hip-hop scene and after being attacked by "Muslims" (he claimed a gang broke his nose – a claim the prosecution may test with an x-ray) and became the "ultra-nationalist" he considers himself today.

Like many who came of age in the late 1990s, much of Breivik's education came via the internet. He admitted he had relied extensively on Wikipedia to produce the 1,801-page "compendium" setting out his manifesto before the attacks last year.

He read the English media, misconstruing a Times article from February 2010 to claim that the newspaper reported that a survey had found "3/5 Englishmen believe that the UK has turned into a dysfunctional society as a result of multiculturalism".

He noted that "Sarkozy, Merkel and Cameron have all said that multiculturalism has failed". He had studied recent history and was disgusted to see what happens "any time nationalist parties take power". He cited as examples the partial EU boycott after Jörg Haider's far-right Freedom party entered Austria's government in 2000, and the rightwing coalition in Hungary, which he claimed, was under pressure to "change their mind by being called intolerant nationalist Nazis".

Breivik insisted he was not alone in fighting against mass immigration. He singled out the National Socialist Underground, neo-Nazis who killed nine immigrants and a policewoman in Germany, and Peter Mangs, suspected of a seven-year killing spree in the Swedish city of Malmö.

It was important, he said, that these "heroic young people" should be celebrated for sacrificing their lives for the "conservative revolution".

He also declared himself inspired by al-Qaida, which he described as the most successful militant organisation in the world, and one from which other ultra-nationalists would do well to learn. But he claimed al-Qaida was now emulating the "one-man cell" model he had operated on 22 July with such deadly success.

At the start of Tuesday's court session, one of the five judges was dismissed after it emerged he had posted a message on Facebook last year saying "death penalty is the only just thing to do in this case". Thomas Indebro, 33, one of three ordinary Norwegians sitting as lay judges alongside two professionals, was replaced.

Breivik has four more days to explain why he set off a bomb in Oslo's government district, killing eight, and then gunned down 69 on Utøya. He denies criminal guilt, saying he was acting out of "necessity". On Tuesday, the court-appointed interpreters issued a correction to their translation of Breivik's not guilty plea on Monday.

He is not claiming to have acted out of "self-defence", as originally reported, but is using a defence under section 47 of the Norwegian penal code that states: "No person may be punished for any act that he has committed in order to save someone's person or property from an otherwise unavoidable danger when the circumstances justified him in regarding this danger as particularly significant in relation to the damage that might be caused by his act."