A deadly Mexican prison riot is being scrutinized two years after it occurred following the recent release of security footage from that night. In particular, the guards' apparent lack of concern was being called into question. As rival prison gangs brawled April 27, 2013, leaving 13 people dead and 65 wounded, prisoners climbed over fences and broke furniture while prison guards stood silently watching the riot unfold before them.

At a San Luis Potosi prison in central Mexico, known as "La Pila," a battle broke out between rival gangs the Zetas and the Gulf Cartel with little interference from the guards. After doing little to quell the fighting, guards can be seen later in the video dragging wounded and dead bodies together into a single room. An opponent of the reigning government released the footage as Mexico's midterms elections neared, according to a New York Times report released Friday.

The violence -- seemingly sanctioned by the guards -- suggested the continued dominance of drug gangs in Mexico in spite of the war on cartels begun by Felipe Calderon when he took office in 2006. David Skarbeck, a professor at  King's College London and author of "The Social Order of the Underworld," told the Atlantic in 2014 that "prison gangs end up providing governance in a brutal but effective way...they impose responsibility on everyone." As the rival cartels fight, the guards are powerless from both corruption and fear.

The footage also demonstrated many of the problems of the modern Mexican prison, which are severely underfunded and overcrowded, leading to excessive violence and corruption. There are 242,754 inmates in Mexico in facilities built for a maximum of 195,278, according to government statistics, the New York Times reported. "Mexican prisons are places that tend to produce more criminality, not only because of the overcrowding present in many of them, and corruption, but also because inmates of varying degrees of dangerousness are placed together," according to Leslie Solis, a researcher at Mexico Evalua.

Mexico's National Commission on Human Rights has ranked San Luis Potosi prisons among the worst in terms of safety, overcrowding and prevention of violence, according to The New York Times.