Buddhists? Wiccans? Seventh Day Adventists? A Russian Tim McVeigh with a grudge against the government? Don't be silly. It was jihadis, of course, signaling that the holy war in still a go in a land where apprehended warriors don't get the kind of kid glove treatment they do in the U.S.
What, you think the fact that there's no "Mirandizing" in Putin's domain is going to deter them?