The guards are accused of shooting inmates after a riot broke out in Carandiru prison in Sao Paolo. It began when a group of prisoners took control of a cell block. When armed police re-entered the prison, officers began opening fire on the prisoners, going so far as to allegedly execute some who had been wounded, Amnesty International said.
"This trial must be a turning point," Atila Roque, the human rights group's Brazil Office director, said in a statement. "For years, the delay in bringing those responsible for the Carandiru massacre to justice has been a dark cloud hanging over the whole country -- we hope that now this impunity is finally coming to an end."
The officer in charge of the raid, Col. Ubiratan Guimaraes, was initially convicted in 2002 and sentenced to more than 600 years in prison, but a higher court later overturned the verdict, saying Guimaraes was acting within his legal authority.
The first group facing trial includes 26 rank-and-file officers who allegedly took part in the massacre.