Charged with hunting down Ukrainian saboteurs inside Russia, with keeping anti-Kremlin activists in check, and with disrupting the operations of hostile foreign intelligence agencies, the FSB, the main successor agency to the Soviet-era KGB, has its hands full.
The US has maintained that it has intelligence that confirms that the Islamic State is responsible for the shooting, as they claimed. However, Putin is questioning Washington's stance.
Russian President Vladimir Putin has refused to directly blame the Islamic State for the Moscow concert hall terror attack despite a claim by the extremist group and has implied that the attackers had links to Ukraine.
Intelligence related to the terrorist attack on Moscow has fueled speculation regarding the possibility of state actors having foreknowledge or involvement in the incident.
The Crocus City Hall terrorist attack and shelling of civilians by Ukrainian troops have a common goal to intimidate people, but masterminds behind them and perpetrators will be punished, Russian Prosecutor General Igor Krasnov said on Tuesday