Police were Friday set to interview the man suspected of the attacks a week ago in Norway that left 76 dead, as part of efforts to determine if he acted alone, dpa reported.
Anders Behring Breivik has been charged with the July 22 bombing in the city that killed eight people, and the subsequent attack on nearby Utoya island that killed 68 people. He was remanded in custody Monday and is to undergo a psychiatric evaluation.
Friday was also the day of the first funeral for one of the victims of the attacks, an 18-year-old Iraq-born woman. Other memorial vigils were scheduled including at an Oslo mosque in the presence of Prime Minister Jens Stoltenberg.
Investigators were to question Breivik, 32, about new information received since their first seven-hour interview with him Saturday, prosecutor Pal-Fredrik Hjort Kraby said.
Compiling the case against Breivik was expected to take months.
Tor-Aksel Busch, head of the Norwegian Prosecuting Authority, has said that "out of respect for the dead and next of kin the perpetrator must be tried for each killing," and this would require sufficient documentation.
The acts constituted terrorism since they were aimed at instilling fear in the public at large and could be punished with a 21-year prison term, the prosecution has said.
However, authorities were considering whether Breivik could be charged with crimes against humanity. The maximum sentence for such crimes is a 30-year prison term.
Breivik's lawyer Geir Lippestad expected authorities to move for the longest possible sentence, he told the Aftenposten newspaper.
A priority in the investigation was to establish if Breivik acted alone, Kraby said, adding that Norwegian authorities had received a lot of information and were cooperating with among others the FBI in the United States.
Police are analysing security camera footage of the suspect taken just minutes before the bomb exploded in central Oslo as well as Breivik's computer and online activity prior to the attacks.