The clash of gang members in a Juárez prison last week shocked Mexico and the world. Seventeen prisoners died and four were wounded in a confrontation last Tuesday night when various members of the group Los Aztecas, an armed branch of the Juárez Cartel, were fired upon when they entered the prison by members of Los Mexicles, which is part of the Pacific Cartel. As is usually the case with this kind of incident, the given explanation for the fight was that gang members were fighting for control of the prison. The truth is more complex, and reveals a new chapter in the war on drugs.

What happened in Juárez is part of a consistent pattern of the last five years all over Mexico, where the Mexican penitentiary system has become an extension of the drug cartels’ battlefield. From behind bars, cartel members plot confrontations and even carry out killings. Another pattern has been the escape of prisoners, which has revealed how porous Mexican prisons are, a result of institutional corruption.