I believe this is true from articles I've read. Breivik was a great fan of Geert Wilder, who we know opposed the influx of Muslims.
I’m rapidly becoming of the opinion that he’s a ringer who insinuated himself into those circles in order to discredit them. No Christian kills the innocent intentionally. Leftists do, though. They even have cute euphemisms for it, breaking a few eggs to make an omelet and all that.