With the world politics of the last 50 years... chances are they might have been Muslim. With the break down of ussr and the conflicts in the middle East, and most of that part of the world hating the West...
A person would guess that the Boston sh1t would either be white boys, or religious extremest from that part of the world or middle East.
It's not that some Atheist from Sweden is naturally less violent that a white boy from Chechnya - It's that Chechnya has been fcked over, Islamist picked up the pieces and carried on with the causes.
If the person was atheist, the story wouldn't have been "atheist bomber blows sh1t up".. it would have simply been "crazy emo white boy loser wants revenge against capitalism or bullies" .
We have to wait for more details to come out, but I think most people can see that these boys religion isn't the reason they wanted to blow sh1t up... Chechnya's history alone can tell you that.