Two years after they went missing, the fate of 43 Mexican students who disappeared on their way to a protest in the town of Iguala remains unknown.
Thousands of supporters gathered in Mexico City this week to demand answers about exactly happened on the night of September 26, 2014, when students at a teacher training college in Ayotzinapa disappeared.
The Mexican government says that the case has been solved, but its assessment has been challenged by the students' families, human rights organisations and independent investigators.
In January 2015, Mexico's attorney general, Jesus Murillo Karam, alleged that the government had solved the mystery behind the missing students.
Corrupt members of the local police, said Karam, had handed the students over to a drug cartel, who killed them, burned their bodies at a dump in Cocula, and dumped their remains in a river.
Forensic experts, independent journalists and human rights groups, however, say there is no evidence to support the government claims.
"We analysed the evidence approximately for a year bringing specialists from different disciplines and the conclusion was that there was no evidence of massive killing and burning on that particular site," said Mercedes Moretti, a forensic investigator.
Prosecutors have detained more than 100 police, politicians and drug traffickers in connection with the case, but have convicted none.
Responding to pressure from international human rights groups, the attorney general's office said recently that it would use laser-scanning technology to look for clandestine graves in other locations near the Cocular dump, and investigate if police from other towns were involved in the mass disappearance.
"We can't say that they were killed if we don't have the irrefutable scientific proof, nor tell the parents, 'accept it, they are dead, go back home to mourn your dead'," Vidulfo Rosales, a lawyer representing families of the missing students, told Al Jazeera.
Historian Lorenzo Meyer said the Ayotzinapa case, named after the location of the college in which the teachers-to-be were studying, is one of the darkest chapters in Mexico's history.
"There is no logical explanation for that ending. It is brutality to the extreme of insanity, but that is not spontaneous, it is the product of decomposition of state structures in Mexico for a long time," he told Al Jazeera.
READ MORE: Mexico no closer to solving missing-students mystery
The case brought Mexico to a standstill and called into question President Enrique Pena Neito's credibility as well as the integrity of his government.
Families argue the government is covering up the truth to protect high-ranking officials allegedly involved in the disappearances.
"We don't want any more lies," said Cristina Bautista, a mother of one of the missing students.
"We want to know the truth. Where are our children?"
Families say the restless nights continue, but there is one motto that keeps them going: "They took them alive, we want them back alive."
Source: Al Jazeera News