A security guard and an explosives expert described in court the massive blast that rocked Oslo when Anders Behring Breivik bombed a government building last July, killing eight people.
Tor Inge Kristoffersen, a security guard in the Norwegian capital's government quarter, told the court that on July 22 he saw a white van park at the foot of the tower housing the offices of Labour Prime Minister Jens Stoltenberg.
He said he was in the operations centre in the basement of the building and was using surveillance camera images to check whether the van was authorised to be there.
"When I was zooming in on the number plate, the car exploded," he testified, adding that "half of the images disappeared from our screens because the cameras had been destroyed in the explosion."
"There was a huge roar. We were so close that we did not hear a blast, but a roar, and we noticed the shockwave in the ceiling over us," he said.
Kristoffersen, a former soldier who served in the Middle East and in the Balkans, continued to work in the government district after the attacks, and likened the area to "a war zone."
In the weeks after the bombing and Breivik's subsequent shooting massacre on the nearby Utoeya island -- where he killed another 69 people, mainly teens -- many raised questions about how the right-wing extremist could have parked his van so close to Norway's political nerve centre.
In his testimony, Kristoffersen stressed that long-overdue construction was under way to block off traffic in the street outside the government building, but that in the meantime "illegal parking" was frequent in the area.
"We chased cars away from there every day," he said.
Svein Olav Christensen, a government explosives expert, meanwhile told the court that a reenactment and simulations showed that Breivik's bomb had the energy equivalent of between 400 and 700 kilos (180-320 pounds) of TNT.
"The main charge is easy to make," he said, adding though that "the detonator is more difficult."
The 33-year-old confessed killer used fertiliser, diesel and aluminium to make his 950-kilo bomb, which killed eight people working in the building and passers-by and injured dozens more.
Stoltenberg, who was working from his official residence that day, was not harmed in the attack.
Breivik has said his twin attacks were "cruel but necessary" to stop the Labour Party's "multicultural experiment" and halt the "Muslim invasion" of Norway and Europe.
