It's a fair bet that the snipers were members of Chavez's Bolivarian Circles. They are pro-government neighborhood watch groups set up to inform the government of activities in their neighborhood. Castro proposed the idea when he was in Venezuela celebrating his birthday as Chavez's guest. Chavez has been using them to counter any marches with violence. They've threatened opposition legislators and beaten up reporters. They heavily looted stores after the coup was reversed. Since one reporter was killed and others injured when the marchers were fired on from rooftops, it adds to the belief the snipers were Chavez's thugs, called Chavistas. It has also been speculated they were aided by the 100+ Castro agents in the country who have the run of the security offices. Other Castro exports to Venezuela are hundreds of teachers, sports advisors and doctors.
you'll need to show why they fired on both anti and pro chavez groups for this assertion to hold. i can think of a plausible rational or two, but without some hard evidence, i doubt many would be convinced.