Philip Manshaus, 22, stormed the Al-Noor mosque in an affluent suburb of the city on August 10 before he was overpowered by a 65-year-old worshipper.
One person was injured in the rampage before Mohamed Rafiq heroically apprehended Manshaus.
His step-sister, Johanne Zhangjia Ihle-Hansen, adopted by his father's girlfriend, was later found with three shots to the head at their home. A .22-caliber rifle was found in Manshaus' car.
Police official Pal-Fredrik Hjort Kraby previously revealed how Manshaus' explanation and technical evidence, including the lack of a struggle, 'support the version that she (his step-sister) was killed because of what the attacker considers as race, because she was of Asian origin.'
Rafiq was among three people inside when a man burst in with 'two shotgun-like weapons' and wearing a uniform and body armor.
Police said the suspect was waving weapons while inside the mosque but did not specify what type.
After breaking through a glass door, the gunman fired off a number of shots before Rafiq and Mohamed Iqbal, who helped to subdue the suspect, spotted him.
The retired Pakistani Air Force officer described struggling with the gunman.
afiq said: 'He put the finger inside my eye up to there, the whole finger.'
He was the only person injured at the mosque despite multiple gunshots being fired, according to police.
Prime Minister Erna Solberg called the attempted attack a 'direct attack on Norwegian Muslims.'
Manshaus, who is being held in custody pending formal charges, has admitted to the facts but has rejected the 'terrorist act' and 'murder' suspicions against him.
On September 9, at a court hearing to extend his detention in custody, Manshaus raised his arm in a Nazi salute to the assembled media.
Source: The Daily Mail