Some have suggested that the FSB would be capable of recruiting ISIS to do terror attacks in Moscow. That is true but was the concert hall attack a false flag?
A more likely possibility is that it is what it is ...... an ISIS attack motivated by anger at the Putin regime, a desire to create breakaway Islamist Republics within Russia and the Stans and Putin regime weakness ..... as shown by Free Russia rebels in Belgorod.
The CIAs knew an attack was coming but didn't know the details. Putin dismissed the US warning.
My guess is that Moscow security just prioritised their own safety over the safety of the public. They are as dysfunctional as the term Communo-Fascist suggests.
Putin has to blame someone or anyone but ISIS ATM because he can't admit to seeding an Islamist rebellion within Russia.
