The attack was claimed by ISIS-K - a foreign fighter offshoot/offbrand. Funny thing is that ISIS-K fighters were getting lifts from American chanook helicopters in Afghanistan and is largely made up of US assets and/or people formerly trained by the US in Afghanistan.

Lots points to it being a CIA asset, tldr. They're a dirty army that can be used to keep an area distabilised or prevent other geopolitical powers from building infrastructure/influence (the nutshell purpose of ISIS-K, particularly in Afghanistan to prevent pipelines being built).

They had the inside scoop on an attack outside any usual operating theatre by a group with tangible links to US cooperation/orientation? No kidding.

Mr. Bortnikov, the F.S.B. director, said on Tuesday that Islamist extremists alone couldn’t possibly have carried out the attack. He blamed, among others, the United States.

Gee, I dunno how three or four lunatics could acquire guns.