> Now the evidence itself suggested at least a plausible hypothesis: the attacks were triggered when a bus used to transport heroin was commandeered by the students, and that the motive—because the municipal police and others involved in the attacks didn’t know which of the commandeered buses had the drugs aboard, or perhaps had been specially outfitted to smuggle drugs without detection That's a very plausible theor…
Essentially, the students were murdered by the ruling narco-state fusion. The Federal authorities efforts to blame the events on a fusion of local authorities and narcos likely is perceived as an effort to cover up the general collusion between the state and the narcos on all levels.
This is a world in which during the course of the investigation, 60 other mass graves, of other large groups of people murdered in area were found [1]. When industrial-scale for murder and the disposal of bodies are operating, yeah, it's hard to figure out how certain people died and where they are not.
As a cause, I get the impression that finding the students' murderers now is oriented towards not finding some specific hidden villain or exact turn of events but rather on casting light on the entire narco-state complex where corruption goes up to highest level (and extends into the US).
BBC: "Mexico missing students: Search uncovers 60 mass graves" The attorney general's office says the remains of 129 bodies have been recovered from the graves. None of the remains have been linked to the students who vanished in Iguala." [1] http://www.bbc.com/news/world-latin-america-33671636