The garbage dump where remains were found outside the mountain town of Cocula. Photograph by Henry Romero/Reuters

The official scenario, according to the Mexican government, of what befell the forty-three students from the Raúl Isidro Burgos Normal School, in Ayotzinapa, in Guerrero state, on the night and morning of September 26 and 27, 2014, is generally referred to as the “historical truth.” Say those words anywhere in Mexico, and people know what you mean. The phrase comes from a press conference held in January, 2015, when the head of the government’s _Procuraduría General de la República _(P.G.R.) at the time, Attorney General Jesús Murillo Karam, announced that the forty-three students had been incinerated at a trash dump near the town of Cocula by members of the Guerreros Unidos drug-trafficking gang, after being turned over to them by members of the Iguala municipal police. This, he declared, was the “historical truth.”

As had already been widely reported, the forty-three students were among a larger group of militantly leftist students who, that night in Iguala, had commandeered buses to transport themselves to an upcoming protest in Mexico City. They’d driven from Ayotzinapa that afternoon in two buses they’d previously taken, and then, the government said, they took two more from Iguala’s bus station. Three other people were killed in initial clashes with the police, and most likely with other forces, in Iguala that night; many more were injured. According to Murillo Karam, the “historical truth” was partly drawn from the confessions of detained police and drug-gang members, including some who admitted that they had participated in the massacre of the students at the Cocula dump, and claimed to have tended the fire and disposed of the remains afterward. Some of those remains had allegedly been deposited by gang members in a nearby creek. Nineteen severely charred bone fragments had been sent to a highly specialized lab in Innsbruck, Austria, which had yielded one positive DNA identification, of a student named Alexander Mora Venancio. That identification seemed to support the P.G.R.'s story that the students had been killed at the dump.

One problem with the "historical truth" was that the families of the disappeared students, mostly indigenous people from impoverished rural Guerrero, did not accept it. Nor did many others who’d been closely following the case. On the day in November when P.G.R. investigators had recovered the remains from the nearby creek, including the bone fragment later identified as belonging to Mora Venancio, the internationally prestigious Argentine Forensic Anthropology Team (E.A.A.F), which was collaborating with the Mexican government, had not been summoned. The organization declared that it could not verify or account for the chain of custody of those remains. The Mora Venancio bone fragment, according to the Argentine specialists, was unlike the others recovered from the site—it was bigger, and not as badly burned, as if it had come through a different fire. The families also protested that the P.G.R.’s explanation discounted the testimony of other witnesses, including students who’d survived the attacks, who claimed that other authorities, including federal police and locally stationed military units, had either participated in or closely observed the actions taken against the Ayotzinapa students that night.

The initial crime inspired huge protests, and its handling by Mexican President Enrique Peña Nieto provoked a worldwide outcry; because of that, along with some other high-profile scandals, the government’s credibility and reputation have been seriously undermined. This may explain why, on November 18, 2014, the government decided to permit an intrusion onto Mexico’s vaunted traditional sovereignty by allowing the Inter-American Commission on Human Rights (I.A.C.H.R.) to appoint a group of five legal experts to conduct, with the P.G.R.’s coöperation, an independent investigation of the Ayotzinapa case.* Murillo Karam resigned, and was replaced, in February of 2015, by Arely Gómez González. The Interdisciplinary Group of Independent Experts (GIEI), a team of five people from Chile, Colombia, Guatemala, and Spain, and consisting of prosecutors, lawyers, a former attorney general, and a social psychologist specializing in victims’ rights, released its first report—which was more than five hundred pages long—on September 6, 2015, nearly a year after the crime was committed. The group’s next, and presumably last, report, will be released on Sunday.

The September 6th GIEI report demolished Murillo Karam’s “historical truth” and made history of its own. Perhaps never before, and certainly not in recent decades, had Mexican government authorities been confronted with such a thorough legal investigation of a crime of such consequence, and of the state’s handling of that crime. Among many other findings, the GIEI report rejected assertions by the government that federal security forces had no involvement in Iguala on that night in September. They credited the testimony of student survivors and other witnesses who alleged that federal police had been present, and had acted aggressively, and most importantly, that the students’ movements had been monitored by the military, beginning from the time they’d left the Ayotzinapa school on the afternoon of September 26th and on into the night. The witnesses also noted the presence of military units in the streets of Iguala. GIEI found evidence, too, that confessions in the case had been elicited by torture. It also discovered security-camera footage from the Iguala bus station that confirmed what some students had claimed all along: that a fifth bus had been taken that night, one that, according to the fourteen students who rode in it, was detained by federal police as it tried to leave Iguala; those students managed to, or were allowed to, escape into the surrounding hills, but the bus itself disappeared. GIEI reported that when it asked to see the bus, it was shown one that, according to the findings of a video-forensics expert in the United States, was not the same one filmed by the bus station's security cameras. GIEI was especially interested in that missing bus because, in 2014, the U.S. Attorney’s office in Illinois had charged two alleged members of the Guerreros Unidos gang with smuggling heroin and cocaine from Mexico to Illinois using commercial buses; the report raised the hypothetical possibility that the overblown aggression against the students had been provoked by a frantic effort by a drug gang and complicit authorities to recover a bus.

The part of GIEI’s September report, however, that received by far the most attention in the Mexican media was centered on the Cocula dump. Dr. José Luis Torero, a Peruvian fire-forensics expert who participated in the 9/11 World Trade Center investigations, and heads the School of Civil Engineering at the University of Queensland, Australia, declared that it was scientifically impossible for forty-three human bodies to have been incinerated at the Cocula dump, under the circumstances described in the confessions by the Guerreros Unidos gunmen who were detained by the P.G.R.

The Mexican government had accepted GIEI’s mission in order to demonstrate that it possessed the will, if not always the capabilities, to investigate, solve, and achieve justice for a crime that had shocked the world. Ayotzinapa became symbolic of so many other crimes that have occurred in Mexico, and epitomized the lawlessness and violence of a drug war that has led to an estimated hundred and fifty thousand deaths and some twenty-seven thousand disappearances. Most crucially, for the families of the missing forty-three youths, GIEI represented a bridge of communication to the legal authorities, as well as protection against the abandonment of relatives and the disparagement of victims that routinely attends such crimes in Mexico. Thanks to GIEI, the Ayotzinapa families even got to air their concerns and grievances in face-to-face meetings with President Peña Nieto.