Police in Norway have so far only said the attack in Baerum, a town 20km from Oslo, the capital, will be investigated as a possible act of terrorism.
In messages posted on the day of the attack, Philip Manshaus, a 21-year-old man who has been named by local media as the main suspect, described himself as “chosen” by “Saint [Brenton] Tarrant”, the gunman who killed 51 people at mosques in New Zealand in March.
“My time is up, I was chosen by Saint Tarrant after all … We can’t let this continue, you gotta bump the race war threat in real life … it’s been fun,” one post reads.
In a meme also posted by Manshaus, three rightwing extremists suspected of being responsible for other attacks this year are depicted and praised as heroes of the white nationalist movement.
Tarrant is described as having “addressed the Muslim problem” while Patrick Crusius, who has been charged with the attack in El Paso, Texas, in which 22 people died, is praised for “fighting to reclaim his country”.
The evidence of posts supporting the actions of the three suspects will fuel fears that a “cascade” of rightwing extremist attacks is gathering supporters around the world.
“We are now no longer talking about one-off events, but a loosely coordinated chain of far-right attacks across the world, where members of these networks inspire – and challenge – each other to beat each others’ body counts,” said Peter Neumann, professor of security studies at King’s College London.
“The ultimate motivation … is to launch a race war. The aim is to carry out attacks, claim responsibility, explain your action, and inspire others to follow.”
The posts, made shortly before the attack, were both reported to have been on a new messaging board called Endchan, which describes itself as “an anonymous image-board that promotes ideas over identity,” and an older board called 4chan.
Unmoderated messaging boards have emerged as a key vector for the spread of extremism.
Neumann said any hopes that shutting down 8chan would deprive the far right of its virtual network looks misguided as supporters quickly move on to other message boards.
Authorities believe Crusius was the author of a racist white nationalist screed that was posted online shortly before the El Paso attack. The author of the document said the attack was “a response to the Hispanic invasion of Texas” and said he was inspired by the gunman in Christchurch.
The post by Manshaus linked to a live stream on his Facebook page – since taken down by the social network.
Witnesses said Manshaus was wearing body armour and was armed with two “shotgun-like weapons” and a handgun.
He was overpowered by people at the mosque before police arrived at the scene. One man was injured in the attack.
Manshaus has been charged with the murder of a woman found dead in his home.