In May 2002, Contreras was convicted as the mastermind of the 1974 abduction and forced disappearance of Socialist Party leader Victor Olea Alegria. He received 15 years in prison on 15 April 2003 for the disappearance of tailor and MIR member Miguel Ángel Sandoval in 1975, although the sentence was reduced on appeal to 12 years. Also in 2003, he was sentenced to 15 years in prison for the 1974 disappearance of journalist Diana Frida Aron Svigilsky. While he was amnestied in 2005, the Supreme Court overturned that decision and confirmed the judgment against Contreras on 30 May 2006. Contreras received another 15-year prison sentence on 18 April 2008 for the disappearance of political dissident Marcelo Salinas Eytel.