It never does any good whatsoever to jump to conclusions when the facts are not all in. Case-in-point:
1.) The Times Square bomber was not a white guy (sorry, Contessa Brewer!)
2.) The IRS plane crash-guy was not a right winger. C’mon, he quoted from the damned Communist Manifesto!
3.) Nidal Hassan wasn’t white, and did not act because of PTSD by proxy.
4.) John Lee Muhammad was not a white guy, and his actions did, indeed, have ties to Islam
Of course, the opposite was assumed in all of the cases above by a slathering, excitable press (who forgot about all four stories the instant they found out that they didn’t fit the “Narrative”).
So, like I said, it never does much to assume things in situations like this. However, I will say that I suspect Chechyn Islamist radicals to be to blame. I also suspect that the reason that they’ve failed to claim responsibility is two fold:
1.) it isn’t necessary – the Russians know.
2.) For purposes of survival, it is a good thing to not spend your time blowing up Russians and then gloating about it. Thy aren’t gentle about their reprisals like we Americans are.