Nicknamed Admiral Zero, Massero was in charge of the Escuela de Mecánica de la Armada (Navy Mechanical School)—perhaps the most symbolic, clandestine detention and torture facility in of the dictatorship era. Many of the individuals who disappeared and were tortured by the junta—estimates range from 9,000 to 30,000 people—passed through the walls of Massera’s Escuela.
After the country’s return to civilian rule, Massera was found guilty of murder, torture and invasion of privacy by the trial of the Juntas reconciliatory body in 1985. Despite being sentenced to life in prison, Massera received a pardon in 1990 for these charges as well as for his involvement in Operation Condor by then-President Carlos Menem. In 1998 he was again convicted, this time of concealing and changing the identities of the children of the disappeared, and was sentenced to house arrest due to his age.
Massera died of cardiac arrest, which was related to a history of neurological problems.