So this guy declared war against muslim immigrants eh? Why do I suspect most of the people he killed were ethnic norwegians?
They were members of the main Norwegian leftist/multiculturalist party; it was a party youth retreat he targeted. His reasoning was that the muslim invaders would never have got a foothold in the nation, without the connivance of the native leftists -- hence native leftists bore greater guilt. By targeting a youth group, he ensured that many of those leftists would never cast even one vote.
Evil. But perfectly logical.