CNN —The four men suspected of carrying out a brutal attack at a Moscow concert hall that killed at least 137 people have appeared in court on terror charges, as the Kremlin defended its security services criticized for failing to prevent the massacre. Shamil Zhumatov/ReutersOn Monday, three days after the attack, rescuers were still searching among the ruins of the collapsed concert hall and trying to clear rubble. CNN has geolocated the 90-second video to the concert hall, where bodies and blood can be seen on the floor as fire rages above. Despite ISIS appearing to provide evidence that its fighters had carried out the attack, Russian President Vladimir Putin has been keen to point the finger elsewhere. Firefighters respond to the burning Crocus City Hall on March 22.

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