The FSB helping the ISIS attackers in carry out their attack by ensuring they had free passage through Russia and free passage to carry out the attack is the most likely scenario..
It is not the first false flag FSB in Russia.
There is no evidence to support Ukraine has aided ISIS, there is no evidence to support Ukraine arresting ISIS members. Accusing Ukraine if being being this ISIS attack is simply an attempt to shift blame from the real culprits, being ISIS and Putin.
