Anders Behring Breivik ... gruesome autopsy details were revealed in court.

Anders Behring Breivik ... gruesome autopsy details were revealed in court. Photo: AP

A court in Norway on Monday heard gruesome details about the deaths of some of the youngest victims of self-confessed gunman Anders Behring Breivik.

Medical examiner Torleiv Ole Rognum presented 12 autopsy reports to the Oslo District Court. They included that of a 15-year-old boy, one of the youngest attending the Labour Party youth camp on the island of Utoya in July.

Each victim was presented with a photo and brief description after their autopsy report was read out.

Breivik showed no emotion as Rognum and police officer Trond Sandsbraten described how the victims had died and the location in which their bodies were found - a building that served as a cafe, dining and assembly hall. Thirteen youths were killed inside the building.

The proceedings were particularly trying for the bereaved and survivors.

"It was tough but we have waited for this," Freddy Lie, father of a 16-year-old girl who died in the building on Utoya, told news agency NTB.

She had talked to him on her mobile phone just before she died.

Lie said he had prepared for the court hearing by reading up on all the reports he could get hold of. But he said he was caught off-guard by a police photo shown in court of his late daughter's mobile phone shot to pieces.

Lie's older daughter, aged 18, survived the gun rampage with serious injuries.

Prosecutor Inga Bejer Engh was visibly moved by Monday's session, according to courtroom reporters, while judge Wenche Elizabeth Arntzen told the bereaved that they were free to leave the courtroom at any time.

Breivik, 33, has admitted to carrying out a bomb attack near the government buildings in Oslo and subsequent shootings on Utoya, but has pleaded not guilty. The July 22 attacks left 77 dead in total.

The court adjourned on Monday after the 12 reports were presented.

Proceedings are to continue on Tuesday with more autopsy reports. The trial opened on April 16 and is scheduled to last until June.