The suspect in the twin attacks that killed 93 people in Norway was a member of a Swedish neo-Nazi Internet forum, a group monitoring extreme-right activity said Saturday.
"He created a profile in 2009, with a pseudonym that can be traced back to his email address," Mikael Ekman, a researcher with the Stockholm-based Expo foundation, told AFP.
It was not possible however to determine when the suspect, named by Norwegian media as Anders Behring Breivik, was last active on the forum, which counts some 22,000 members from across the region, he said.
Nordisk a web forum founded in 2007, describes itself as a portal on the theme of "the Nordic identity, culture and traditions."
It hosts discussions on "everything from white power music to political strategies to crush democracy," Ekman wrote in an article published Saturday on the Expo magazine's website.
Nordisk's members range from Swedish members of parliament for the far-right Sweden Democrats party to Nazi leaders, the article explained.
"What united the members is a critical attitude to the current refugee policy and immigration," it said.
Some contributors to the forum have posted comments inciting violence.
"Cars parked next to high buildings with fertilising powder + diesel gives a nice effects," one anonymous user said last year on the forum.
"The buildings go down like the World Trade Center."
"I think it's a but too bad that people do not see this is a war we must wage," the contributor, who Ekman said was not Behring Breivik, added.
"Those ... in government, who do not live close to or don't have to experience immigrants' threat in their nice neighbourhoods ... in my world there is no dishonest act one can commit against these monsters," the user wrote.
On Sunday, Norwegian police confirmed that a 1,500-page violent anti-Islamic manifesto was published by Breivik just hours before Friday’s attacks.
The online book describes the planning, explosives making and violent philosophy that lead to the bombing in downtown Oslo and shootings at a Labor youth camp nearby.
"This manifesto was published on the day of the events," Oslo's acting police chief Sveinung Sponheim told a news conference. "We have confirmation of that."
The killings would draw attention to the manifesto, called "2083-A European Declaration of Independence," Breivik wrote.
"Once you decide to strike, it is better to kill too many than not enough, or you risk reducing the desired ideological impact of the strike," he wrote.
He also attacked "the Islamic colonization and Islamisation of Western Europe" and "rise of cultural Marxism/multiculturalism."
"He wishes to change society," Breivik's lawyer Geir Lippestad told public broadcaster NRK.
The lawyer earlier said that his client "believed the actions were atrocious, but that in his head they were necessary."
The lawyer also said that his client wanted to explain himself in court on Monday.
86 people were killed when a gunman dressed as a policeman opened fire at a youth camp hosted by the ruling Labour party's youth wing at an island near Oslo.
7 people were killed in a bomb explosion that hit government buildings in the centre of the Norwegian capital.