Restrained by a harness, the Norwegian reconstructed his actions for police in a secret daylong trip back to the crime scene at Utoya island near Oslo.
A prosecutor also confirmed Norwegian media reports that police received several phone calls during the attack that were probably from Breivik himself, but wouldn't say how police had reacted to the calls.
According to Norwegian daily Aftenposten, Breivik offered to surrender several times and asked police to call him back, but they didn't.
Police said they took Breivik back to Utoya for a Saturday hearing about the attacks on July 22, when Breivik shot the victims at the lake island after killing another eight people in the capital with a bomb.
Breivik's lawyer has said he has confessed to the terror attacks, but denies criminal guilt because he believes the massacre was necessary to save Norway and Europe from Muslims and punish politicians who have embraced multiculturalism.
The 32-year-old Breivik described the shootings in close detail during an eight-hour tour on the island with up to a dozen police, prosecutor Paal-Fredrik Hjort Kraby told a news conference in Oslo.
The hearing took place amid a massive security operation that aimed to avoid escape attempts by Breivik and protect him against potential avengers. Breivik walked roughly the same route as the one he took during the shooting spree and explained what happened with as little interference as possible from police, Hjort Kraby said.
The entire hearing was filmed by police and may later be used in court, he added.
Video images of the reconstruction published by Norwegian daily VG show Breivik arriving at Utoya with the same ferry he used to get to the island last month. Breivik wore a bulletproof vest and a harness connected to a leash over a red T-shirt and jeans as he casually led police around the island.
Breivik is seen pointing out locations along the way and simulating shots into the water, where panicked teenagers dove in to try to escape from him.
"The suspect showed he wasn't emotionally unaffected by being back at Utoya ... but didn't show any remorse," Hjort Kraby told reporters. "He has been questioned for around 50 hours about this, and he has always been calm, detailed and collaborative, and that was also the case on Utoya."
The hearing was arranged to avoid the need for a reconstruction in the midst of the trial and to make Breivik remember more details, Hjort Kraby said.
Norwegian media have also reported that Breivik may have filmed parts of the massacre himself. Hjort Kraby said Sunday that a video camera had been discussed during the hearing on Utoya, but declined to elaborate.
Prosecutors have previously told The Associated Press that Breivik owns a video camera that they are still trying to locate, but have dismissed reports they received witness statements about Breivik filming on Utoya.
Initial speculation suggested others were involved in the terror attacks, but prosecutors and police have said they are fairly certain that Breivik planned and committed them on his own.
Breivik faces up to 21 years in prison if he is convicted on terrorism charges, but an alternative custody arrangement - if he is still considered a danger to the public - could keep him behind bars indefinitely.