A panel of international experts on Sunday accused Mexico's government of undermining their probe into the fate of 43 trainee teachers apparently massacred in 2014, the most notorious human rights case in Mexico in recent years.
The independent panel said the government's stonewalling stopped them from reaching the truth as they wrap up their work and prepare to leave Mexico.
The attorney general's office, they said, did not let them re-interview detainees accused of the crime or obtain other information in a timely fashion. Prosecutors did not pursue investigative angles that the experts suggested.
"The delays in obtaining evidence that could be used to figure out possible lines of investigation translates into a decision (to allow) impunity," the report by the experts, commissioned by the Inter-American Commission on Human Rights (IACHR), said.
At a 2-1/2-hour news conference on Sunday attended by more than 1,000 people, the experts cast doubt on aspects of the government's version of events and said they had been repeatedly blocked in their efforts to obtain evidence from Mexican authorities.
Mexico's government says that corrupt police in late 2014 handed the student teachers in the southwestern city of Iguala over to drug gang henchmen, who believed the trainees had been infiltrated by a rival gang. They then incinerated them at a garbage dump in the southwestern Mexican state of Guerrero.
The remains of just one of the 43 students has been identified from a charred bone fragment. The government said it was found in the San Juan river, by the town of Cocula, near Iguala where the students disappeared.
The panel said that the government's theory the students had been burned is scientifically impossible given the heat needed to reduce human remains to ash.