These wolves are not outsiders. They are native to Norway.
Brevik killed Norwegians, in opposition to immigration. He did not directly kill outsiders.
This is not a one-off event. The Norwegian government has done this before. From 2001, http://www.cbsnews.com/news/killing-wolves-in-norway/
> A Norwegian government team killed the fourth of nine wolves ordered felled in a hunt that has outraged conservationists and Swedish officials. ...
> Norway ordered the nine shot after complaints from local farmers of wolves killing livestock and pets, and wandering into farms and villages in a zone designated as wolf-free.
> Conservationists and Swedish officials have objected to the hunt, saying there are still so few wolves that killing nearly 10 percent of the stock is irresponsible.