Mr Breivik, wearing a bulletproof vest and tethered on a rope, was seen pointing to where he had fired shots. Police later said he showed no remorse.
Mr Breivik’s attacks on 22 July also killed eight people in an Oslo bombing.
The 32-year-old far-right extremist admits the killings but denies any criminal guilt.
Norwegian prosecutor Paal-Fredrik Hjort Kraby said Mr Breivik described the killings in detail during his eight hours on the island with police.
“Regarding the suspect’s explanations, he has been interrogated for almost 50 hours prior to this and he has remained calm, detailed and co-operative, which he also was at Utoeya,” he said.
“Our assumptions that his presence at Utoeya would jog his memory was correct. Many new details emerged from his explanations.”
Mr Hjort Kraby said some of the victims had drowned while trying to swim to safety.
Police filmed the reconstruction to use in evidence, Mr Hjort Kraby said.
Mr Breivik’s lawyer, Geir Lippestad, says Mr Breivik believes the massacre was necessary to save Norway and Europe from Muslim immigration. The lawyer has said his client is probably insane.
Newswarped thinks that the autorities are insane for taking Breivik back to Utoeya Island and letting him relive his killing spree for eight hours.
He is guilty. The police response was inadequate. What else is there to say. It is almost ghoulish to have him getting the chance to do it all again for the camera’s.
On Friday, Mr Lippestad said his client had called police 10 times during the shootings to try to turn himself in, but that eight were not answered. The police have not commented. They were probably too busy doing ‘death tours’ with Anders.