It is now the second deadliest terror attack in Russian history.
US intelligence confirmed ISIS' claim of responsibility. And the US said it had warned Russia of the attack ahead of time.
Putin says all four individuals have been captured. There are videos of the suspects being tortured. One had his ear cut off by FSB agents.
Naturally Putin says Ukraine was helping the terrorists and arranged for them to cross into Ukraine. But the terrorists were heading towards Belarus not Ukraine.