Thousands of protesters gathered in Mexico City on Tuesday, angered by the government's handling of an investigation into 43 students who apparently were massacred in 2014 and the government's alleged treatment of international experts who have cast doubt on the official account.
The case of the 43 trainee teachers, who were abducted in September 2014 in the violent southwestern state of Guerrero, has tarnished the reputation of President Enrique Pena Nieto and highlighted the scale of human rights abuses in Mexico.
The parents and relatives of the abducted students led what appeared to be more than 2,000 protesters along the main thoroughfare of the Mexican capital, Paseo de la Reforma, carrying small torches along with large black and white photographs of the missing students.
Blanca Luz, the mother of one of the 43, said she wants to meet with Pena Nieto to discuss the investigation, a request frequently echoed by the parents.
"My heart can't take anymore," she said, standing near the main building of Mexico's attorney general's office. "I want my son back by my side."
The government has repeatedly said the students were abducted by corrupt police in the town of Iguala on the night of Sept. 26, 2014, who handed them over to a drug gang. The cartel then burned the students in a nearby dump, a government investigation concluded.
But an international panel of experts, commissioned by the Inter-American Commission on Human Rights (IACHR), has published a series of reports casting serious doubt on that account.
In its final report published on Sunday the panel said the government had undermined its probe and accused it of stonewalling efforts to uncover the truth.
The panel, known as the Interdisciplinary Group of Independent Experts (IGIE), said it had been repeatedly blocked in efforts to obtain evidence from Mexican authorities and said the attorney general's office did not let its members re-interview detainees accused of the crime.
Prosecutors did not pursue investigative angles that the experts suggested, the panel added.
Speaking in Geneva on Tuesday, United Nations human rights spokesman Rupert Colville expressed concern about the experts' claims and urged Mexican authorities to explore the lines of enquiry they suggested.
"The main concern at present is that with the departure of the IGIE, there's unfinished business," he said. "There's clearly much more to be done and the final resolution of the case doesn't appear to be that close."
At a press briefing on Monday, U.S. Department of State spokesman John Kirby commended the experts for their work on the investigation and said he hoped the government would incorporate their suggestions into its investigation.
"We call for the completion of a full and transparent investigation of the students' disappearances and the prosecution of all those responsible," he said.