Manshaus was armed with a hunting rifle and a shotgun and fired four shots with the rifle at a glass door before he was overpowered by one of the men in the mosque at the time, Muhammad Rafiq.
During the scuffle, two more shots were fired but no one was hit. Rafiq was slightly injured in the struggle. In his testimony, Manshaus said he wanted to kill Rafiq.
"I did everything I could to carry out the attack," he told court, adding he was exhausted when police arrived.
The prosecution says Manshaus acted "with the intention to kill as many Muslims as possible".
The video recorded by his helmet was played in court Thursday. NRK said it showed Manshaus shooting at the mosque door before kicking it open. An elderly man — Rafiq — is then seen walking toward him and Manshaus is heard yelling: "You should never take over Norway."
Minutes later, when the suspect has been overpowered and is on the ground, Manshaus is heard moaning and begging to be killed, saying: "I can't do anything more. I am faithful to my people." The camera is facing the ceiling.
Some 30 witnesses, including the men at the mosque and Manshaus' father, are expected to give evidence.
If found guilty, Manshaus could face up to 21 years in prison. The prosecutor has said it would consider a sentence where he would be sent to a secure mental facility for as long as he is considered a danger to others.
Norwegian media have reported that Manshaus was inspired by shootings in March 2019 in Christchurch, New Zealand, where a gunman targeted two mosques, killing 51 people, and in August 2019 in El Paso, Texas, where an assailant targeted Hispanics and left at least 22 dead.
Manshaus' plans and his reference to national socialism also recall those of Norwegian right-wing extremist Anders Behring Breivik, who in 2011 killed 77 people in a bombing and shooting rampage. Breivik, who gave a Nazi salute in the court room, is serving a 21-year prison sentence for carrying out a terror attack.
Norway's domestic security agency PST said it had a "vague" tip about Manshaus a year before the shooting, but it was not enough to act on because they had no information about any "concrete plans" of attack.
- AP