Anders Behring Breivik (L) sits in the rear of a vehicle as he is transported in a police convoy as he is leaving the courthouse in Oslo July 25, 2011. [Agencies]

OSLO - Norway's police believe Anders Behring Breivik probably acted alone in killing 76 people last Friday, and Norwegians united in revulsion against the worst attack in the Nordic nation since World War Two.

A source close to the investigation told Breivik's talk of other cells: "We feel that the accused has fairly low credibility when it comes to this claim but none of us dare to be completely dismissive about it either."

Researchers also doubt Breivik's claim that he is part of a wider far-right network of anti-Islam "crusaders," seeing them as empty bragging by a psychopathic fantasist who has written that exaggeration is a way to sow confusion among investigators.

On Tuesday, Justice Minister Knut Storberget will meet police chiefs who are facing criticism for taking more than an hour on Friday to stop a shooting spree in which 68 people, mostly teenagers, were shot after a bomb in Oslo killed eight.

Norway has felt a widening sense of relief that 32-year-old Breivik seems to have been alone in his drive to protect Europe from "cultural Marxism" and a "Muslim invasion" by striking at Norway's ruling Labour Party.

More than 100,000 Norwegians rallied in Oslo on Monday night, many carrying white and red roses, to mourn the dead and to show unity after July 22. Tens of thousands of others rallied in other cities from Tromsoe to Bergen.

Border Controls

In signs that police are toning down fears that Breivik was part of a wider network, border controls imposed on July 22 were lifted late on Monday. Norway has not asked foreign nations to launch probes nor raised the threat level for terrorism.

Even the final entry in Breivik's own 1,500 page manifesto says on July 22: "The old saying: 'if you want something done, then do it yourself' is as relevant now as it was then."

"Intuitively, it feels like he is alone when you read the document. It's like he's lost in this made-up world and can't distinguish between fantasy and reality," said Magnus Ranstorp, Research Director at the Center for Asymmetric Threat Studies at the Swedish National Defense College.

"They (mass killers) are usually alone," he said.

Police defended themselves from suggestions that some alarm bells should have rung about Breivik. The head of the PST security police even said he would have slipped through the net in former East Germany with its feared Stasi police.

PST says Breivik's name appeared only once, on a list of 50-60 Norwegians sent by Interpol after he paid 120 crowns ($22.16) to a Polish company that sold chemicals and was on a watch list. They found no reason to react.

Stasi Germany

"I don't think even Stasi Germany could have uncovered this person," PST chief Janne Kristiansen told the VG newspaper's online edition, adding he was "the incarnation of evil."

Breivik is likely to face a lifetime in jail if convicted of the crimes, which included shooting dead terrified teenagers on Utoeya island at a Labour Party summer camp.

He admits the attacks, but denies criminal responsibility. Even his father is horrified.

"In my darkest moments, I think that rather than killing all those people, he should have taken his own life," Breivik's father told Norwegian independent TV2 in France.

He said his son, with whom he has had no contact since he was a teenager, must be mentally ill. "There is no other way to explain it."

Other researchers say that he shares traits with past mass murderers.

"He has no empathy, he is indifferent to the people he kills, he has no conscience and no remorse," said Ragnhild Bjoernebekk, a researcher at Norway's police school.

"Evil can kill a person but never conquer a people," Norwegian Prime Minister Jens Stoltenberg said on Monday evening at the mass rally, probably the biggest in Norway since the end of World War Two. Norway's population is 4.8 million

"Our fathers and mothers promised 'never again April 9'. We promise 'never again July 22'," he said. Hitler's forces invaded Norway on April 10, 1940 at the start of a five-year occupation.

Many Norwegians have expressed relief that Breivik seems to have been a lone, home-grown fanatic rather than, for instance, an envoy of al Qaeda. Many compare him to Timothy McVeigh who killed 168 people with a truck bomb in Oklahoma City in 1995.

"If this was done by a foreigner it would have been very difficult," said Raj Pereet Singh, a Norwegian whose parents immigrated.