Police said they took Anders Breivik back to the island of Utoya Saturday in a special hearing about the July 22 terror attacks.
Breivik is accused of shooting the victims dead on the lake island near Oslo after killing another eight people in the capital with a bomb.
The 32-year-old described the killings in close detail during an eight-hour tour on the island with up to a dozen police, prosecutor Paal-Fredrik Hjort Kraby told a press conference in Oslo.
The special hearing took place amid a tight 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 reconstruction was filmed by police and may later be used in court.
The Associated Press contributed to this report.