The suspect in the shooting at a mosque outside Oslo held far-right, anti-immigrant, views. The young white male is suspected in the murder of his stepsister, authorities said.
The suspected shooter, a white male in his 20s, had expressed far-right, anti-immigrant views online, assistant chief of police Rune Skjold said in a news conference.
In particular, the suspect had expressed support for Vidkun Quisling, a Norwegian politician who collaborated with Nazi forces when Germany occupied Norway during World War II.
Norwegian media reported on Saturday that the suspect was believed to have praised the Christchurch, New Zealand, shooter in an online forum hours before the attack.
But the authenticity of the post or the exact identity of its author has not yet been established.
He also allegedly supported the man suspected of a shooting in a southern California synagogue in April, and the man accused of fatally shooting 22 people at a Walmart in El Paso, Texas, earlier this month.