My initial reaction to this is that while elements of it may be true, it cannot be the entire story. I'm not sure exactly in what order the news the trickled out, but I first heard about it as just evidence that the Gómez prisoners were sneaking out at night, and then it morphed into the story they were sneaking out to perpetrate the most brutal crimes in the Laguna since Pancho Villa executed a whole bunch of Chinese during the Mexican Revolution. If the sequence in which I heard about reflects how the news story developed, it just seems too neat by half. Even if the story broke all at once and I just heard about it parts, it just seems implausible that people would repeatedly massacre innocents and then go hide from the authorities in jail. That seems much closer to a Robert Rodriguez version of Mexico than something that would happen real life. And what is the advantage for the gangs' ultimate bosses, who are presumably not in prison, in using inmates for killers? Are there not gang-members on the outside who are available for this sort of thing? Wouldn't using the prisoners just increase the chance that this turns into a major story and as such a priority for the federal government, which spells bad news for the gangs?
Furthermore, there were reports after the second of the three main massacres in Torreón this year, in May at a bar called Las Juanas, that four of the killers were apprehended and beheaded by people associated with the bar. If those reports are true (and they may not be, but they were quite common after the shootings, some of which included photos of the heads), wouldn't we have already have had reports of four supposed prisoners killed on the streets of Gómez Palacio after having participated in a mass killing?