3-5 heavily armed men casually strolled into a concert with assault rifles and explosives, killed dozens of people, set off multiple explosives, with no security in sight, after the west already warned Russia an attack like this was coming but Russia did not step in security, despite the fact that Moscow is one of the most surveillance cities on Earth and where you get arrested just for holding up a sign.
Something tells me Russia let this happen, even with it being a legit terrorist attack.