The overall toll in the attack now stands at 76 instead of 93 — still one of the worst modern mass murders in peacetime.
Police spokesman Oystein Maeland said that higher, erroneous figure emerged as police and rescuers were focusing on helping survivors and securing the area, but he did not immediately explain more about how the overcounting occurred.
Police also raised the toll from a bombing outside the government's headquarters in Oslo before the shooting spree, from seven to eight.
Anders Behring Breivik has confessed to both assaults but denied criminal responsibility for them and pleaded not guilty at his first hearing. He told the court he wanted to save Europe from Muslim immigration and warned that there are two other cells of his terror network.
The court ordered him held for eight weeks while prosecutors investigate, four of which will be in isolation, saying Breivik could tamper with evidence if released. Typically, the accused is brought to court every four weeks while prosecutors prepare their case, so a judge can approve his continued detention. Longer periods are not unusual in serious cases.
Breivik made clear in an Internet manifesto that he planned to turn his court appearance into theater, preparing a speech for his appearance in court even before launching the attacks, then requesting an open hearing in which he would wear a uniform. Both of those requests were denied.
The suspect has said staged the bombing and youth camp rampage as "marketing" for his manifesto calling for a revolution that would rid Europe of Muslims.
"The operation was not to kill as many people as possible but to give a strong signal that could not be misunderstood that as long as the Labor Party keeps driving its ideological lie and keeps deconstructing Norwegian culture and mass importing Muslims then they must assume responsibility for this treason," according to the English translation of Heger's ruling that was read out after the hearing.
Breivik alluded to two other "cells" of his network — which he imagines as a new Knights Templar, the medieval cabal of crusaders who protected Christian pilgrims in the Holy Land. At one point, his manifesto briefly referred to an intention to contact two other cells, but no details were given.
European security officials said they were aware of increased Internet chatter from individuals claiming they belonged to the Knights Templar group and were investigating claims that Breivik, and other far-right individuals, attended a London meeting of the group in 2002.
Reporters and locals thronged the courthouse on Monday ahead of the hearing for their first glimpse of Breivik since the assault. When one car drove through the crowd, people hit its windows and one person shouted an expletive, believing Breivik was inside.