Santiago de Chile, January 9 (RHC-teleSUR) -- A Chilean judge sentenced 23 former agents from Chilean dictator Augusto Pinochet's secret police to prison Thursday for their role in the forced disappearance of a left-wing activist following the 1972 coup that overthrew Salvador Allende's government.

Among those sentenced was General Manuel Contreras Sepulveda, who was in charge of Chile’s notorious National Intelligence Directorate (DINA).

This is only the latest sentence for Contreras, who has been found guilty in numerous other cases of human rights violations. He has been sentenced to serve a total of 400 years for his crimes.

Six of those sentenced will serve 13 year terms, while another 15 will serve ten years. Two others, who played an accomplice role, will serve four years.

Bernando de Castro, who was a member of the President Allende's Socialist Party of Chile, was disappeared after being arrested by the DINA. De Castro was disappeared along with four others whose bodies have yet to be found. Their forced disappearance was part of a cover-up coordinated by Chile's secret police forces, known as “Operation Colombo.”

As part of the cover-up, magazines sympathetic to the dictatorship published articles claiming that 119 political prisoners had been killed in “internal purges” of the Revolutionary Left Movement, the MIR, which had launched an armed struggle against the U.S.-backed Pinochet dictatorship.

Chile’s justice system has been working to process claims by victims of the dictatorship, however only 10 percent of Pinochet's former agents are serving prison sentences.