Accusations of U.S. involvement in Moscow attack surface

Nikolai Patrushev, head of Russia's National Security Council, accuses the U.S. of involvement in the Moscow concert hall attack that killed 144 people. ISIS Khorasan claimed responsibility, while Ukraine denies involvement. Four suspects were arrested in the Bryansk region, bordering Ukraine. Russian officials claim the attackers planned to flee to Ukraine. The U.S. Embassy warned Russia of potential attacks, including at Crocus City Hall.