sentences:  Though, once again the masks they wear are said to ward off possible retribution from criminals, police or Chavez's political opposition, but they also reinforce an imposing image that critics call a tool of intimidation against Chavez's political opposition.Some have claimed that the Tupamaros execute such criminals because they are competition and they want to have control.Luis Milan, a political science professor at Bolivarian University talked about a riot that began when police opened fire.