Anders Behring Breivik yesterday gave a chilling account of his shooting massacre on the Norwegian island of Utoeya last year, explaining in detail how he calmly executed terrified teens.

“I lifted my weapon and I shot him in the head,” Mr Breivik told the court of his first victim on July 22 on Utoeya, where he shot 69 people dead after first killing eight people in a bombing of government buildings in Oslo.

Before launching into the part of his testimony most dreaded by the many survivors and victims’ relatives watching his trial, the 33-year-old right-wing extremist warned people who did not want to hear the “gruesome” details to leave.

None did.

He went on to explain that when he arrived on the island, where the ruling Labour Party’s youth wing was hosting a summer camp, he had been reluctant to go through with his plan, saying that the minute he spent trying to decide whether or not to shoot “seemed like a year”.

“My whole body tried to fight against... there were a hundred voices in my head saying ‘Don’t do it! Don’t do it!’,” Mr Breivik, who was dressed as a police officer at the time, told the court.

But after he lifted his gun and shot down his first victims, an off-duty police officer and the camp administrator, there was no more hesitation. He said he calmly walked up towards a café building, which was full of people and where he killed 11.

“I thought: ‘Now I am going into that building and will execute as many people as possible in that building,’“ he told the court coldly as survivors, families of his victims cried quietly.

Mr Breivik, who yesterday wore a black suit and shirt with a silver tie, said he did not remember everything from the shooting spree.

Yet at times he provided devastatingly detailed descriptions, saying in one room he first shot a group of four or five people, all in the head.

“I think many are screaming and begging for their lives,” he said, seeming to sneer slightly as he recalled how some of the people in the room were “paralysed”.

He then turned to another group on the other side of the room.

“I don’t know why there were still people in the room at this time,” he said, before adding “I shot them all.”

Many of the victims received several bullets to the head and back.

He explained without emotion how he consistently used “follow-up shots,” shooting most people several times to make sure they were dead, noting that “some of them were playing dead. That’s why I fired so many times.”

Mr Breivik insisted he was not without a conscience, pointing out that he did not shoot a young girl and a young boy on two separate occasions since he estimated they were younger than 16.

His youngest victim that day had just celebrated his 14th birthday.

He also said he had considered suicide. “I thought: do I really want to survive this? ... I will be the most hated person in Norway ,” he said.

In the end, however, he said he decided he could better spread his nationalistic, Islamophobic ideas if he lived to tell his story in court.