Norwegian police are verifying if twin attack suspect Anders Behring Breivik was the author of a manifesto and a video which appeared on the web, Norwegian media said.
The 32-year old ethnic Norwegian on Saturday confessed to killing over 80 people on the Utoya Island Saturday evening. Breivik is also believed to have been one of those linked to the Oslo bombing, which left seven people dead.
"We confirm that some information appeared on the web," Einar Aas, the head of organised crime department of Oslo Police, told Norway's TV2 channel.
"We are studying it now."
The document, headlined "A European Declaration of Independence", is written by Andrew Berwick, but the author says in the text this is an anglicised version of Anders Breivik.
In the 1,500-page document the author expresses his extreme anti-Muslim political views and describes the attacks which are to be carried out.
It describes how to make bombs from fertilisers and how to receive them in large quantities by setting up an agricultural company.
The author says he emailed it to thousands of people, mostly his "patriotic Facebook friends" and their friends. He says it took him nine years to write the manifesto, reflecting his background and political views.
The manifesto also contains previously unknown Breivik's pictures.
A person who identified himself as Andrew Berwick also uploaded a video on YouTube calling calls for conservatives to "embrace martyrdom", six hours before the bomb in the centre of Oslo went off.
The 12-minute video, called "Knights Templar 2083", also reportedly appeared on Breivik's now-closed Facebook page.