Russia has long worried about terrorism. The Moscow attack showed it may not be prepared.

The horrific slaughter at Crocus City Hall, in which gunmen with automatic weapons and explosives killed over 130 people last Friday, has jolted Muscovites out of a sense of complacency that they have enjoyed, despite two years of war in next-door Ukraine.

In an address to Russians the day after the attack, President Vladimir Putin hinted that Ukraine might have been involved in the atrocity.

But he failed to mention a more plausible suspect: the group known as Islamic State Khorasan (ISIS-K), a sworn enemy of Russia generally associated with the kind of ruthless, face-to-face massacres that