Promise 4 guys money if they live and 70 virgins if they don't. Hand them 4 AKs, ammo, some petrol bombs, and tell them to go shoot up a concert hall. If they don't make it there's plenty more where they came from.
If the concert hall is in Kabul, sure. Operationally, there's a little more to it to get it done in Moscow.
Sure, ISIS (main branch) has managed to get some ops done in mainland Europe, mostly in France and Belgium (lots of easy to radicalize Muslims there) but they've been hit pretty hard by more recent uptick of violence in the mid-east proper and have been having problems even spinning up the lone wolves for 3 or 4 years now. ISIS-K, which I've seen mentioned hasn't ever struck outside their home geography.
Could they have done it alone? Sure, with some luck. But it's not a conspiracy theory to point out that A coordinated attack in Moscow, with an exfiltration plan and coordination with another country to receive them is outside the operational capabilities ISIS has previously shown, and not really consistent with their previous attack's TTPs (use local migrants that have been radicalized and martyr them).
It bears noting that ISIS has released some video from inside the attack that wasn't publically available to bolster their claim of responsability. That would imply either live streaming back to ISIS PAO, or someone living long enough to email a video file, something that while not technically difficult, is new for ISIS, and dangerous.
I guess the real question is not was ISIS involved, but were they aided. If they were not aided in this attack what caused the shift in operational capabilities, and can they carry that shift to other targets. If they were aided, who did it, and do we care enough to prevent that from happening again?
