As a self-appointed satellite photo analyst, I should point out that the photo lacks time and context and is below the threshold of making any kind of identification.
Violence by guards and inmates happens as a daily matter in a megaprison. If this is part of the same prison complex, then chances are high that it demonstrates violence that occurred to some other unfortunate persons or animals (the photo lacks resolution so badly that even human vs. animal identification is hard to make).
(a larger photo should be published to provide context, and would be easy to publish for a person interested in proving things, so I caution against trusting the source too much - the source might be more interested in spreading a rumour that goes viral)
These guys are likely still alive. But the chances of getting resistant tuberculosis in an El Salvadorian megaprison are extremely high. Besides gang and guard violene, spending time there can bring about a death sentence of a slow and paintful kind - carried out by bacteria that will reliably overcome a human immune system.