@Lustig Andrei,
The lack of claim of responsibility is weird - if it's organised terrorism.
'We are punishing you imperialist dogs/infidel scum/libtard bastards/right wing nutjobs for... sorry can't tell you, don't do it again.'
Kind of defeats the purpose of terrorism I would have thought.
What is also odd is that in days gone past you would have got several groups claiming responsibility (if this had happened in other parts of the world where it's more common).
I'm leaning to lone wolf - but I have less idea than most. Am pretty confident that the perp will be tracked though, but maybe I've watched too much american crime drama.