Philip Manshaus, 22, wore a dark suit and appeared at a court hearing outside Oslo. He made an "OK" sign with his hand when he entered the courtroom. Such signs have been used by some people as a symbol of white supremacy.
Manshaus is accused of murder and committing acts of terrorism. He was arrested on August 10, 2019 after firing at the Al-Noor Mosque on the outskirts of Baerum, Oslo.
Only three worshipers were in the mosque at the time of the shooting and there were no serious injuries when a 65-year-old man defeated Manshaus after the action.
The body of Manshaus' stepbrother named Johanne Zhangjia Ihle-Hansen, 17, was found in their home by police with four bullets hit. According to police, the victim was shot dead before Manshaus attacked the mosque.
Johanne Zhangjia Ihle-Hansen was adopted from China by her father's girlfriend.
Manshaus has admitted the facts about the case, but he pleaded not guilty. He, as quoted AFP, claiming his actions were "must".
According to prosecutors, Manshaus had racist motives and was inspired by the attack in Christchurch in New Zealand in March 2019, when Brenton Tarrant killed 51 people in shootings in two mosques.
During the trial in court about the extension of his detention, Manshaus paid Nazi respect to the press.
The trial will continue until May 26. He faces 21 years in prison if convicted.