On the night of September 26, 2014, not quite a year ago, municipal police from Iguala in the southern state of Guerrero opened fire on a caravan of commercial buses wending its way through the city’s downtown. The moral and political crisis provoked by the incident has not only endured, it has grown steadily worse. In the latest development, an investigation backed by the Organization of American States concludes “no evidence whatsoever exists” to support key aspects of the Mexican government’s findings.

What’s known is this:

In the mayhem after the police opened fire, the bus passengers ran for their lives. Most of them were student activists at a rural teachers college in Ayotzinapa; three were shot to death that night, along with a taxi driver, his female passenger, and a semiprofessional soccer player riding with his team in another bus. One of the students killed, a 19-year-old named Julio César Mondragón, was found horribly mutilated on the street, his face peeled from the skull, and his eyes plucked out.

In the hours and days to follow, the students who survived “The Night of Iguala” resurfaced back at the teachers college. But 43 of their classmates remain unaccounted for to this day. Eyewitnesses say they were rounded up by police and driven away in haste. It was the first presumed massacre of this kind in Mexico since the Dirty War of the 1970s, and the longer the government of President Enrique Peña Nieto persisted without tracking down the disappeared students, the more severe the political crisis became.

There were vibrant, occasionally massive street protests staged all over Mexico throughout the fall, the spirit of the protests spreading to a number of countries abroad, including the United States. One indelible image from that time occurred on November 20 at the end of a rally in the Zócalo in Mexico City, when several thousand protesters massed in front of the National Palace chanting in unison for President Peña Nieto to resign. At the front of the crowd, several Molotov cocktails were lobbed at the palace, and several hundred riot police charged the crowd and fired tear gas while protesters stood their ground. Many of them could be heard singing the national anthem.

On January 27, 2015, after four months of turmoil, Mexico’s attorney general, Jesus Murillo Karam, officially declared the 43 students dead. He said they were kidnapped by local police and executed by a local drug gang that then burned the bodies to ashes in a garbage dump in the neighboring town of Cocula. The drug cartel supposedly had mistaken the college students for a rival gang of hardened criminals known as Los Rojos. As far as the government was concerned, it was an egregious case of mistaken identity, and the boys had been disappeared without a trace.

This was, in the attorney general’s unforgettable words, “the historic truth” that families of the students would have to accept. But the parents of the disappeared Ayotzinapa students put no stock in Murillo Karam’s announcement, which they dismissed as an exercise in political expediency. And two weeks later, on February 6, an independent forensics team from Argentina, brought in to conduct a parallel investigation at the parents’ invitation, publicly disputed the Mexican government’s version.

As the one-year anniversary of the Ayotzinapa massacre draws near, the historic truth of January is in tatters.

Last week, on Sept. 6, the Inter-American Commission on Human Rights, part of the Organization of American States, released a 560-page report on the Ayotzinapa massacre.

Mexico had agreed to cooperate with the commission in November, granting its panel of five legal experts access to documents, witness statements, and other evidence from the criminal investigations, and permitting them to interview some witnesses and government officials. The findings of the panel’s investigation are so devastating to the Mexican government’s credibility they led a spokesman for Amnesty International in Latin America to declare that the report “exposed the utter incompetence and unwillingness of the government to find and punish those responsible.”

In the first place, the Inter-American Commission found that “no evidence whatsoever exists” to support the Mexican government’s claim that the bodies of the students were cremated at the trash dump in Cocula. The fuel available at the dump would have been insufficient to burn a single body, much less 43, according to José Torero, a professor in fire safety engineering at the University of Queensland (Australia) and a member of the Australian Academy of Technology and Engineering consulted for the report.

The Inter-American Commission report also represents the first attempt by investigators to determine the role of the Mexican security forces during the Ayotzinapa massacre. Until now, the role of federal police and army at the scenes of the shootings and disappearances has not been fully investigated. Contrary to what Attorney General Murillo Karam said at the time, state and federal police and the Mexican Army were present during the massacre and tuned in via a central radio frequency during what the investigators determined were nine separate armed assaults on the students.

The new report concludes that Mexican security forces at the state and federal levels knew the students were under attack and did nothing to protect them. Radio transmission records obtained from the night of the massacre indicate there was radio chatter between the various security forces at the start of the shooting. No sooner had the radio chatter gotten underway, however, than it abruptly died down, with the authorities maintaining radio silence for the next two hours—the two hours in which the students were abducted and ultimately disappeared. The report states that the Mexican Department of Defense denied panelists full access to the radio communications. In any event, the security forces did not resume on-air communication until around midnight.

What is more, Mexican security forces had been keeping tabs on the student protesters since the time that afternoon when around 100 of them departed from Ayotzinapa for the 150-mile journey to Iguala on September 26.

When the students staged a protest takeover of the tollbooths at the highway entrance to Iguala, their movements were being constantly monitored by the military and federal police. The purpose of the tollbooth takeover was to raise money for travel to a march in Mexico City to commemorate the anniversary of the Army massacre of students at the Tlaltelolco Plaza that occurred on October 2, 1968.

Likewise the security forces knew of the students’ plan to commandeer commercial buses for transportation to the demonstration. This move in particular, the Inter-American Commission suspects, may have provoked “high-level interests” in Iguala to react with a level of force which the report deemed neither appropriate, “necessary, rational, nor proportionate.”

Witness statements collected by the Inter-American Commission place Army intelligence agents in at least two of the scenes where the students were stopped by municipal police and ultimately disappeared.

According to further witness testimony cited in the report, one of the buses carrying students was stopped not by municipal but rather federal police. “The car is the classic one they use, the Mustang which says ‘FEDERAL’ on the side. When they got out, I saw their dark blue uniforms, they were federal police,” one witness is quoted as saying. In another instance, a group of Mexican soldiers interrogated students who had taken a wounded fellow of theirs to a private clinic for medical treatment.

One Army intelligence agent was witness to the attacks and detention of students in front of the Palace of Justice in Iguala. Soldiers with the 27th Battalion, the witness said, returned to the scene on board two Cheyenne pickup trucks, under orders to patrol the area and “to specifically avoid confronting the students from Ayotzinapa.” Video surveillance footage of the area in front of the Palace of Justice was destroyed. The Mexican Government declined to make members of the 27th Army Battalion available to the panel of international legal experts.

The gloomy hills that surround Iguala are known to conceal plantations of opium poppy. According to an indictment recently unsealed in U.S. District Court, members of the Guerreros Unidos drug cartel used commercial buses to smuggle heroin and drug proceeds from Guerrero to Chicago. One of the panel’s recommendations to the Mexican government is to investigate whether one of more of the buses were secretly carrying narcotics or drug proceeds.

Of particular interest to them was the existence of a fifth bus seized by the student protesters. The fifth bus was a point of contention between federal investigators, who counted only four buses, and state investigators who counted five. The commission report, however, confirms the existence of a fifth bus, which it states was the only bus not violently attacked by the municipal police in Iguala. At least one mention of the fifth bus appears in the investigation of state authorities, but it is omitted from the federal case file.

The Inter-American Commission raises the possibility that the motive for the overwhelming use of deadly force against the students could have been a load of drugs or drug proceeds concealed in the fifth bus. The panel of international experts reported that when it requested to examine the bus, however, the Mexican attorney general’s office showed them a different vehicle than the one that appears in security footage from the bus terminal on the night of the massacre. The panel also mentions an interview it conducted with a man identified as the driver of the fifth bus, whose testimony it found to be at odds with that of other witnesses, as well as the video surveillance footage.

The findings of the Inter-American Commission’s report open the door to the possibility that the attack on the students was a coordinated operation with the participation of Mexican security forces.

First, the international experts described a suspicious degree of coordination between municipal police forces from the towns of Iguala and Cocula in the armed assault on the students. “The level of intervention of different police agencies… supposes an extant command and coordination for carrying out said action. The operational necessity of coordination between two different municipal police forces… that participated in joint fashion that night indicate the necessity for a degree of central coordination for giving the orders,” the report states.

Then there is the testimony of one of the bus drivers who said that after separating from the students he was taken by police to a white house with a black gate in the center of Iguala, not 15 minutes from the shooting, and presented to “a man with an athletic build,” who ordered him released.

“One of the survivors said that a driver was taken to a safe house in the center of Iguala, and introduced to a man who ran the operation or made decisions on the actions to be taken prisoners. This modus operandi points to a command structure, with operational coordination,” the report states. No further information is known about the man or the house, and the Mexican government does not appear to have pursued this line of investigation.

The report goes so far as to encourage the attorney general’s office to assign new investigators who are open to reinterpreting the facts of the case, and not wedded to any of the grossly flawed conclusions of the Mexican government’s investigators. “We ask the Mexican authorities to clarify the disappearance of the students and to make a general reassessment of the entire investigation,” said Carlos Beristain, one of the five members of the panel.

Within hours of the report’s release, President Peña Nieto took to Twitter to respond. He wrote: “I have given instructions so that investigations of the tragic events of Iguala take into account the data provided by the GIEI [The Interdisciplinary Group of International Experts].”

Arely Gómez González, the current attorney general of Mexico, announced that she intends to extend the mandate of the Inter-American Commission in Mexico. Gómez called the panel of experts’ work “crucial” and stated that the Mexican government was “sensitive” to the findings and “acting decisively before these lamentable acts; the investigations will continue to their final consequences.”

But the factual implications of the Inter-American Commission’s report are serious indeed, suggesting the involvement of two main pillars of Mexico’s state security: the Army and Federal Police. The degree to which President Peña Nieto and Attorney General Gómez are paying lip service to the findings in the report will be determined by the degree to which the Army and Federal Police are made available to the commission in the next phase of its investigation.