Members of the notorious Zetas drug cartel turned the prison where they were being held in northern Mexico into a death camp where they tortured and killed around 150 people, and then incinerated the bodies or dissolved them in acid, the authorities say.
José Ángel Herrera, the chief prosecutor for cases of disappeared people in the state of Coahuila, made the allegations on Wednesday while announcing warrants to arrest five of the prisoners allegedly involved — at least some of whom are still behind bars.
Herrera said that the investigation refers to the period between 2009 and 2012 when the Zetas had near complete control of the prison near the city of Piedras Negras, just over the border from Eagle Pass in Texas.
He said this week's arrests for the atrocities allegedly committed in the prison relate to the cases of the first seven disappeared people who investigators believe they have confirmed were among the victims. That proof, however, relies primarily on information from dozens of interviews with imprisoned witnesses and some of those involved, rather than on physical evidence.
According to José Juan Morales, spokesman for the investigation, the Zetas were allowed to leave the Piedras Negras prison at night to kidnap their victims, sometimes wearing fake police and army uniforms.
The remains of those killed were then, the investigation found, dumped in the nearby San Rodrigo river and in the Rio Bravo estuary.
But while the authorities say they have found bones in the river, they add that these are in such a bad state that it has not been possible to identify whether they came from the prison, or belonged to any of those who might have died there.
The five suspects named this week include Ramón Burciaga Magallanes, the alleged ringleader of the operation inside the prison. He is currently being held in another prison about 300 miles south in the city of Saltillo, the state capital.
Morales said it was clear that the prison guards were at least complicit, though none have yet been arrested. "The guards had knowledge of the facts," he told Reuters.
The three years of terror in the Piedras Negras prison apparently ended around the time of a mass breakout from the jail in September 2012, when 131 inmates escaped in one night.
At the time of the prison atrocities, Coahuila was one of Mexico's most violent states and its jails were overflowing with cartel members who ran the show. The state was also known for its particularly high number of people going missing.
While this case is particularly extreme, Mexico's human rights ombudsman has said that six out of 10 prisons in the country are controlled by members of organized crime.
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