The far-right fanatic, who has admitted to the massacre and a bombing in Oslo on July 22, listened impassively as lawyers for the bereaved read emotional statements and showed pictures from the victims' lives alongside the coroner's autopsy reports.
"We will fight for your ideals, we will see each other again," the family of 17-year-old Lejla Selaci said in a statement read to the court by their lawyer, Thomas Benestad.
Selaci, whose family is from Kosovo, was the leader of a local chapter of the Labor Party's youth wing, which celebrated its annual summer camp on Utoya when Breivik opened fire with a rifle and a handgun. She was shot twice in the head.
In his introductory remarks, coroner Torleiv Ole Rognum said the median age of the 69 Utoya victims was 18.
"The wounds were very special," Rognum said, adding that Breivik used three different kinds of ammunition for the rifle, most of which was designed to fragment inside the victims' bodies.
Breivik, 33, sat motionless in court as lawyers moved themselves and many listeners to tears with their descriptions of his victims.
Attorney Berit Borgen choked back tears as she read a message from the son of Trond Berntsen, a 51-year-old off-duty police officer who was Breivik's first victim on Utoya: "Daddy, you were the best in the world."
Breivik has said he considered the Utoya camp a legitimate target because he claims the Labor Party betrayed Norway by supporting multiculturalism. Breivik claims he is an anti-Muslim resistance fighter on a campaign to protect Norway's cultural identity.
He drove to Utoya after setting off a car bomb outside the government headquarters in Oslo, killing eight.
Since he has admitted his actions, Breivik's mental state is the key issue for the trial to resolve.
If found guilty and sane, Breivik would face 21 years in prison, although he can be held longer if deemed a danger to society. If declared insane, he would be committed to compulsory psychiatric care.
The trial is expected to last through the end of June.