Mexican President-elect Andres Manuel Lopez Obrador on Wednesday promised the parents of 43 students who went missing in 2014 to create a commission to investigate the case, on the anniversary of their suspected massacre.
Four years on, the unsolved disappearance of the students from the Ayotzinapa teachers' college in the southern state of Guerrero still haunts Mexico.
It has become a symbol of the gruesome violence rocking the country, and a stain on the human rights record of the man Lopez Obrador will replace, outgoing President Enrique Pena Nieto.
Speaking after meeting with the students' parents, the leftist president-elect vowed to work to unravel the case starting from the day he takes office.
"On December 1, if it has not already been done, we will sign a decree to create an investigative commission and define the procedures we will follow until the truth is found and justice is done," said Lopez Obrador.
"We also agreed to throw open the doors of the next government and the country to the international human rights organizations that have battled to prevent this case from being closed and enabled us to get closer to the sad, regrettable facts," he told journalists.
- Unsolved mystery -
The 43 students were enrolled at a rural teachers' college known for its tradition of rowdy demonstrations for left-wing causes.
On the night of September 26, 2014, they commandeered five buses to travel to a protest -- a long-standing tradition at their school -- and were attacked and then detained by municipal police in the city of Iguala, Guerrero.
According to federal prosecutors, corrupt police officers then handed the students over to hitmen from the drug cartel Guerreros Unidos, who slaughtered them and incinerated their bodies at a garbage dump.
However, independent investigators from the Inter-American Commission on Human Rights who carried out a forensic analysis of the supposed crime scene found that version of events was impossible.
There was no sign that such an enormous bonfire had burned at the site, they said.
The government's failure to clarify the case has caused widespread speculation about an elaborate cover-up.
The independent experts hypothesized the students may have inadvertently hijacked a bus loaded with heroin bound for the United States.
In a country known for murky links between powerful drug cartels and corrupt officials, that has raised questions about who could have been behind such a shipment.
The case has drawn international condemnation of Pena Nieto's government, which continues to insist on the prosecution's version of events, which it dubbed the "historic truth."
- 'Untenable' case -
The students' parents had urged Lopez Obrador to deliver on his pledge to do justice in the case.
"We'll never find out what happened if we just use the ordinary means of the (Mexican) justice system," said the parents' lawyer, Vidulfo Rosales, ahead of the meeting.
The United Nations meanwhile repeated its criticism of the government's official version of events, calling it "untenable."
"It is worrying that the government has focused on reiterating the untenable and trying to silence or discredit voices who question it," said the Mexico office of the UN High Commissioner for Human Rights in a statement.
Mexico has seen an explosion of crime in recent years linked to brutal violence by drug cartels.
Last year, the country registered a record 28,702 homicides, and grisly discoveries of mass graves have become a regular occurrence.
