Brazil on Tuesday marked the 20th anniversary of a prison riot in which not a single police officer involved in the killing of more than 100 inmates has been convicted. The three-hour uprising at Sao Paulo’s Carandiru prison broke out October 2, 1992, during a brawl between rival groups. It quickly spread to other areas of the facility, which was built to hold fewer than 4,000 inmates but was housing nearly 8,000. The prison was torn down 10 years after the so-called “Carandiru Massacre”. The nearly 100 police officers who took part in the killings are to stand trial early next year. Law professor Oscar Vilhena of Sao Paulo’s Getulio Vargas University said some police commanders involved in the massacre have been promoted, “sending a message that the killing was OK and underscoring the impunity that prevails.” The only police officer tried in the killings was Colonel Ubiratan Guimaraes, who was sentenced in 2001 to 632 years in prison for using excessive force when he ordered police to quell the rebellion. But a Sao Paulo state appeals court overturned the conviction in February 2006 based on arguments that Guimaraes was only following orders. Guimaraes was found dead in his Sao Paulo apartment seven months later with a gunshot wound to the chest. His girlfriend was charged with homicide and is expected to be tried later this year.