Relatives and friends of the 43 missing students wait to hear the results of an Inter-American Commission on Human Rights probe into their disappearance in Mexico City on September 6, 2015
Mexico City (AFP) - Last year, Mexican authorities declared that the "historic truth" in the disappearance of 43 students was that a drug gang killed them and incinerated their bodies in a garbage dump.
But independent investigators from the Inter-American Commission on Human Rights ripped apart the government's conclusions in the case, reviving the mystery about what happened to the young men.
Here is what we know and don't know, almost a year since the teachers-in-training vanished on the night of September 26-27 in the southern Guerrero state city of Iguala:
WHAT WE KNOW
The young men had headed toward Iguala on buses that they had hijacked -- an illegal yet common practice by the students, known as leftist radicals who use the vehicles for their activities.
This time the students -- most of them freshmen -- were going to Iguala to raise funds and take more buses for an October protest.
The official and independent probes agree that the students from the Ayotzinapa teacher training college were attacked by police officers from Iguala and nearby Cocula.
Three students were killed when officers shot at their buses while three bystanders died when a soccer team's bus was also attacked.
Students were whisked away by the police and the fate of 42 of them remains a mystery. Only one of the missing students has been confirmed dead.
More than 100 people have been detained, including municipal officers, drug gang suspects, and the mayor of Iguala and his wife.
WHAT WE DON'T KNOW
Are the students dead or alive?
The commission said it regretted not being able to solve what happened to the 43 students.
The attorney general's office declared last year that the police handed them over to the Guerreros Unidos drug cartel, which killed them, incinerated their bodies in a garbage dump in Cocula and threw the ashes in a river.
But the commission rejected that conclusion.
A fire expert said that nearly 60 tonnes of wood, tires and diesel would have been needed to turn 43 bodies into ashes but that there was no evidence of such a massive fire.
On Monday, the attorney general's office defended its investigation, insisting that at the very least a "large" number of the 43 students were incinerated there.
The charred remains of the only student who was identified, Alexander Mora, were found in the river. But the commission said the bones were discovered an hour's drive away.
The commission's report throws the motive and those responsible for the disappearance into doubt.
Prosecutors have said that Iguala's then mayor, Jose Luis Abarca, ordered the attack because he feared that the students would disrupt a speech by his politically-ambitious wife.
Once in the hands of the Guerreros Unidos, the gang confused the students with their rivals, Los Rojos, according to the official investigation.
But the independent experts say that the students arrived in Iguala after Abarca's wife had spoken, and that there was no reason for the unarmed students to have been confused with cartel members.
The commission offered its own theory: The students may have inadvertently hijacked a bus used by criminals to transport heroin to the United States.
The existence of a fifth bus taken by the students was never included in the official probe, the commission said, adding that it could be a key element in the case.
Another open question is the exact role of the army and federal police that fateful night.
The commission asked the government to investigate whether they failed in their obligation to protect the students even though they had been monitoring their movements and knew they were under attack.