"If he acted alone,"
As your own examples have made clear, whether he acted alone or not is so far a matter of opinion, and couldn't be anything else given the short time since the incident took place. I have no idea whether he had help within Norway and have no opinion on the matter.
I have pointed out that he has claimed to have been in touch with groups outside Norway, including Paul Ray, ex-English Defence League and The Knights Templars, and that his statement has been confirmed by Ray, who has been questioned by the British police - presumably because they believe it to be possible.
Perhaps today's Daily Telegraph might help understand why the "implications are greater than for attacks by lone Jihadists?".
Jim Carroll

Norway attacks: Is the man who inspired Breivik a Briton?
After killer Anders Breivik claimed that he had a mentor in Britain, fears are growing that terrorism from far-Right extremists is becoming a real threat here.
By Gordon Rayner and Matthew Holehouse
7:30AM BST 30 Jul 2011
Could it happen here? From the moment it became clear that the gunman who carried out the world's worst mass shooting was a white supremacist, the question facing every political leader in the West was whether they had been blind to the threat of terrorism from the far Right.
Anders Behring Breivik may be "insane", as his lawyer put it, but he is certainly not alone in his paranoid hatred of multiculturalism, nor is he the first extremist to believe that murdering his countrymen would make him, in his own words, "a hero".
David Copeland, let's not forget, murdered three people and injured 129 when he detonated three nail bombs in London in 1999 during a 13-day campaign targeting the black, Bangladeshi and gay communities. Since then a stream of British fascists has been convicted of plotting similar bomb attacks they believed would trigger a race war aimed primarily at the spread of Islam.
So it should have come as no surprise, perhaps, that Breivik was in regular contact with supporters of the English Defence League (EDL), the latest far-Right group to crystallise around a hard core of anti-Islamification extremists. The EDL is mentioned 29 times in Breivik's manifesto. He claimed to have 600 EDL supporters among his Facebook friends. Almost inevitably, London was the city where he claimed to have embarked on his "crusade" after joining a secret society of anti-Islamic "martyrs".
His description of the inaugural meeting of the "Knights Templar", originally a medieval Christian order that is now a symbol for far-Right extremists, appears to have been written by someone who has swallowed a Dan Brown novel: there are rituals involving skulls, candles and signatures in blood; ancient noms de guerre (Breivik's was Sigurd the Crusader) and a Masonic hierarchy for members."

PS
Ake:
"Just be careful what you wish for Jim."
Sorry - don't follow you - threat - promise - what?
I do understand that your responses so far are remarkably similar to those of the EDL - surprise-surprise!!