- Numerous events are scheduled nationwide to mark the first anniversary
- The twin attacks kill 77 people, including 69 at a youth summer camp
- The nation will also mark a moment of silence at the exact time the bomb detonated in Oslo.
(CNN) -- A year ago, a man bombed a government building in Oslo before heading to an island summer camp, where he opened fire as terrified youth jumped into water to escape the hail of bullets.
The twin attacks killed 77 people, including 69 at the Labour Party summer camp.
Numerous events are scheduled nationwide Sunday to mark the first anniversary of the worst atrocity on Norwegian soil since World War II.
Events in Oslo and other cities include religious services and wreath-laying ceremonies to pay tribute to victims of the attacks. The nation will also mark a moment of silence at the exact time the bomb detonated in Oslo.
Anders Behring Breivik is on trial on charges of voluntary homicide and committing acts of terror in the July 22, 2011 attacks.
He admits to the massacre, and gave chilling details of the gun rampage during his trial this year.
Without apparent emotion, he recounted firing more bullets into teenagers who were injured and couldn't escape, killing those who tried to "play dead" and driving others into the sea to drown.
Some survivors and relatives of victims in the courtroom wept as they listened to his detailed account of the attack on the youth camp on Utoya Island.
Breivik told the court he had made use of lessons learned from al Qaeda in planning his attacks, and was inspired by the Oklahoma City and World Trade Center bombings. He boasts of being an ultranationalist who killed his victims to fight multiculturalism in Norway, and says he acted out of "necessity."
Experts' assessment of Breivik's sanity will be a factor in determining what punishment he receives if convicted. Sentencing options could include imprisonment or confining him to a mental facility.
His verdict is expected August 24.
