I won't point any fingers (yet), but everytime I see the "well, Christianity used to be really violent too!", my blood boils. In WHAT WAY does that excuse what is happening now? If, for example, a black man murders someone, is this excusable with "well, white people are murderers too!". It's not even related.
I'm also ashamed about the fact that I have to point this out, but my statement of a black / white person above has NOTHING to do with my own views on any "race", if you even wish to put people into different "races". The example works even if you change places of the black and white man.
Keep in mind, I'm not defending christianity, islam, buddhism, ANYTHING. Nor am I blaming anything. I just want to point out the ignorance of the argument in itself.
On topic: I really hope there won't be more attacks of this kind. Norway is a great example of a successful country, and they haven't done jack to deserve this as far as I am informed of.
I wish you the best of luck from your neighbour, Sweden!