It seems the OP has made up his mind: religious people are the ones who did it (based on the OP and his second comment).
It seems to be the most likely outcome. When was the last time there was an atheist terrorist attack? I can't think of a single one. Could I be wrong? Sure, I could be wrong. The likelihood of that in this case seems very, very small. An instruction book that says to kill people who don't believe the same as you, plus a belief that no matter what you do, as long as you accept Jesus (or Allah, or Yahweh) as your savior you gain eternal salvation, has led to extraordinary amounts of violence.
Opinions mean shit.
Except that some opinions have the advantage of being correct, or at least are reasonable hypotheses based on an extensive history of violence for religious reasons. If someone were to say "This must have been the result of atheists!" they would have no historical precedent which to point to as evidence.
Stating them as fact(s) makes them worse.
The words "postulate" and "prediction" are hardly statements of fact. I wonder, if/when it does come out that this terrorist attack was perpetrated by a religion person, will you gracefully accept that I was right? Time will tell.
No matter who did it: it's a tragedy, and should, somehow, be prevented in the future.
I can agree with that. It is horrible that people feel entitled to behave in this fashion. My point, in case you missed it, is that EVERY TIME something like this happens, it is a religious person who is responsible. Atheists don't fly planes into buildings, or set off car bombs, or blow up abortion clinics, or shoot girls in the head for trying to get an education, or participate in honor killings, or gun people down in churches. Sure, it's not a known fact yet that a religious person was responsible. But to act like that is not the most likely explanation (by far) is really grasping at straws. Is it bold of me to assume that religion played a role in this? Maybe, but I would be pleasantly surprised if I were wrong. Here
is a list of terrorist attacks committed by Muslims. Here
is a list of terrorist attacks by Christians. Here
is a list of terrorist attacks committed by Jews. I'd post a list of terrorist attacks committed by atheists, but I couldn't even find one. Imagine that.
Ask yourself an honest question: If, when more is known about what happened, and culpability is established, will you be surprised, for even a fraction of a second, if the person responsible is religious? If that is the case, as almost all terrorist attacks are, can we then have a grown up discussion about how religion encourages such violence? Or will the religious be allowed to sweep it under the carpet by labeling the person "Not a true Christian" or by saying that it was done "For political/social/territorial reasons", or by saying that the person must have been insane? Or will we finally be able to admit that religious people are the largest producers of indiscriminate explosions in public places, and start addressing this ghastly problem?