Moscow police said the men "attacked police officers and tried to seize their weapons"
Three defendants have been shot dead after reportedly trying to grab guns from guards during a trial at Moscow Regional Court.
Russia's Investigative Committee said the incident happened when five handcuffed defendants were escorted by two guards in a lift.
Moscow police said the men "attacked police officers and tried to seize their weapons".
They added that "three of the prisoners were liquidated and two wounded".
The two wounded defendants were disarmed and detained.
The defendants were reportedly members of the Grand Theft Auto gang, which took its name from the computer game.
Nine gang members, including the ones who were killed, are on trial charged with the murders of 17 car drivers between 2012 and 2014.
They are also accused of two attempted murders, illegal production and possession of weapons and documents theft.
A lawyer told the Russian news agency a woman bailiff and an armed guard were injured during the attack.
"I saw a wounded woman bailiff, her face in blood. Later somebody said that an armed guard had been injured," she said.