Who are 'El Credo' and 'El Z27'?

A clash between two rival groups led by Jorge Iván Hernández Cantú, 'El Credo', and Juan Pedro Salvador Saldívar Farías, 'El Z27', left 52 dead and 12 injured at the Topo Chico prison in Monterrey, Nuevo León, governor Jaime Rodríguez said.

'El Credo' is considered one of the leaders of the Gulf Cartel and allegedly controlled part of the prison. He was arrested in November 2012 in Monterrey as part of an operation that resulted in the capture of 24 members of a criminal gang that confessed to at least 48 murders, according to local media.

Prison sources consulted by EFE said that an escape attempt organized by members of the criminal group Los Zetas to which Saldívar belongs could be behind the mutiny after they lost control over the premises.

'El Z27', who became regional chief of Los Zetas cartel, was arrested in late 2013 and identified, along with his brother, as the perpetrator of the murder of David Hartley, an American citizen, in September 2010. He could also be involved in the attack against the office of the Immigration and Customs Enforcement (ICE) agency in San Luis Potosí.

Los Zetas were the armed wing of the Gulf Cartel until March 2010, when they split from the cartel, and have since violently fought for territories.

At a press conference the state governor "ruled out an escape attempt as well as the use of firearms."

Topo Chico, one of the oldest prisons in Nuevo León, has about 3,800 inmates.