OSLO — Kept on a police leash, the man responsible for Norway's worst post-war bloodshed showed no remorse when he took part in an eight-hour reconstruction of his island massacre, police said Sunday.

"He was not unaffected, but he showed no remorse for his actions," police prosecutor Paal-Fredrik Hjort Kraby told reporters in Oslo a day after investigators brought Anders Behring Breivik to the scene of his July 22 rampage on the island of Utoeya.

He shot dead 69 people, many of them teenagers.

Just hours before the shooting spree, which he has confessed to, the 32-year-old rightwing extremist also bombed government offices in the Norwegian capital, killing eight other people.

Hjort Kraby said Saturday's site visit had been vital to the case.

"All research shows that it helps the memory to come back to the scene of the crime. (Behring Breivik) provided us with a lot of new information which we didn't have before, despite 50 hours of (previous) interrogation," the police prosecutor said.

"We feel we have a fairly good overview of how everyone died or was shot now, even though there are still details to fill in," he said, adding some of the victims had died had drowned trying to swim for safety.

Behring Breivik was taken to the island some 40 kilometres (25 miles) from Oslo, first by car and then by the same boat he used on the day of the attacks.

The trip on Saturday afternoon was made under heavy security, with Behring Breivik shackled on the boat and kept on "a leash" while on the island, police said.

The self-confessed killer, his lawyer Geir Lippestad and all the police officers wore bullet-proof vests, officials said, and media reported that police helicopters had circled above amid fears of an attempted revenge attack.

Hjort Kraby told AFP that Behring Breivik had clearly been "taken back to that day," when he attacked a summer camp hosted by the ruling Labour Party's youth wing.

"He remembered new things," he said, adding there were no major inconsistencies in his account although "sometimes he would walk in the wrong direction and then correct himself."

"Everything he said was video filmed and recorded" and would be used as evidence in the case, Horst Kraby added.

The police prosecutor confirmed weekend news reports that authorities had Behring Breivik x-rayed a few days after his arrest on Utoeya for fear he may have swallowed an explosive device or remote control.

"We were dealing with a man who had exploded a bomb and who went on to commit many more serious crimes on Utoeya and we had to think of all the possibilities, including that he had swallowed a device," Hjort Kraby said.

He added that police had been worried the killer might try to blow himself up at his first court appearance three days after the attacks or set off a bomb somewhere else, "but the (x-ray) examination was swiftly done and we didn't find anything."

Behring Breivik has said that targeting Prime Minister Jens Stoltenberg's Labour Party was part of a "crusade" to halt a "Muslim invasion" and multiculturalism in Europe.