Norwegian right-wing extremist, Anders Behring Breivik, has admitted he "cannot conceive" what it is like for others to consider what he says are his "gruesome" acts, as his trial continues in Oslo.
On trial for killing 77 people, he will be questioned over his gun rampage on Utoeya island, where the majority of his victims died.
Breivik, who admits the killings but denies criminal responsibility, says his targets - most of whom were teenagers - were those responsible for "multiculturalism".
Breivik says he failed in his plan to kill all 600 people at a Labour Party summer camp last July and behead a former Norwegian PM.
Breivik has admitted shooting 69 people on the island, mostly teenagers, as well as killing eight in a bomb blast in Oslo.
Arriving in court earlier on day four of his trial, Breivik made no far-right salute, as he had on previous days. His lawyers had asked him not to salute. He then gave a graphic account of his intentions, causing some in the public gallery to leave the court in tears.
The BBC's correspondent in Oslo says he spoke calmly, almost proudly, as he described his intention, which was to kill everyone at the Labour Party youth camp, and not by shooting them all: he had calculated that most of his victims would drown in the waters around the island attempting escape.
The waters, he said, were to have been his weapon of mass destruction.
He named former Norwegian prime minister Gro Harlem Brundtland - who had been visiting the camp - as his primary target. He planned to capture and then decapitate her using a bayonet and knife, and post a video of it on the internet.
As it turned out, Mrs Brundtland had left the island before he arrived.
Three bomb attacks initially planned
Earlier Breivik revealed that his original plan had been for three bombs targeting the government, the Labour Party HQ and the Royal Palace. But he found it harder than expected to make explosives, he said, and settled for one car bomb and one gun attack.
"I stand for Utoeya and what I did, and would still do it again," he said - as survivors and victims' relatives cried quietly, shaking their heads in disgust.
However he insisted he was not a "child murderer".
"I believe that all political activists who choose to fight for multiculturalism are legitimate targets," he said. "And 44 out of the 69 people [killed on the island] had leadership positions."
"Does this also apply to the 14- and 15-year-olds?" the prosecution asked.
"It is not desirable to focus on people under the age of 18 but there was no other desirable political target on that day," Breivik replied.
'Extremely difficult' to kill so many
Asked what it was like to carry out such a rampage, he said it was an "extremely difficult" thing to do, as it went against human nature in many ways.
Breivik has admitted the killings but denies criminal responsibility, saying he acted to protect Norway and Europe from multiculturalism and Islamification.
The court is seeking to determine whether Breivik is sane. If so, he will be jailed for at least 21 years, although that sentence can be extended.
If he is deemed insane, he will be committed to a psychiatric institution.
Breivik's evidence is scheduled to last five days, concluding next Tuesday. The entire proceedings are expected to last 10 weeks.