Russian vice-consul Marcos Cesar Feres Braga was targeted by a motorcycle gang as his motorcade waited for the torch procession to pass.
The muggers smashed the car window and pointed a revolver in Mr Braga’s face demanding his watch.
His wife and daughter who were also in the car watched on in horror.
But the diplomat who is trained in jiu jitsu wrestled the gun from the carjacker’s hand and shot him dead at a close range.
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The torch relay had just passed by on Avenida das Americas in the Barra da Tijuca district of Rio, Brazil close to the Olympic Park and athletes’ village – when the gunman struck.
Olympic cyclists from Slovenia were passing by on a training exercise at the time.
Mr Braga reportedly hauled the mugger named as Leonardo Lopes Batista into his BMW X6, disarmed him and shot him dead with his own weapon.