good to see Melo, Yasor, Jem, Arvin, and other members from Norway are OK. Hope all ends well regarding you friends, Jem.
At this point, I wouldn't exclude this being an act of domestic terrorism and unrelated to any islamic extremist groups, even though it is tempting to think otherwise. Those tweets might be just an attempt to take credit and advantage of a already existing situation to send a canned message and instill fear.
Chances are it will turn out to be international terrorism but still, something to keep in mind, I guess.
Hopefully the number of the victims will be limited and this isn't just a sign for things to come.