Independent experts investigating the 2014 disappearance of 43 Mexican students said Tuesday that the state was responsible for the concealment of vital information, making it impossible to continue their work.
The commission, created in 2014 under an agreement between Mexico and the Inter-American Commission on Human Rights, released a sixth and final report on one of the country's worst human rights atrocities.
The experts were unable to continue their investigation given the "concealment and insistence on denying things that are obvious," said Carlos Beristain, a Spanish member of the Interdisciplinary Group of Independent Experts.
The withholding of information "has become a responsibility of the state," he told reporters.
The experts again questioned the actions of the Mexican army in the case, which shocked the country and drew international condemnation.
"Not only did it allow the attacks to happen, but it later covered up and did not provide truthful information about what occurred," the report said.
The students at a teacher training college had commandeered buses in the southern state of Guerrero to travel to a demonstration in Mexico City before they went missing.
Investigators said that they were detained by corrupt police and handed over to a drug cartel, though exactly what happened to them is unclear.
Last year, a truth commission tasked by the government to investigate the atrocity branded it a "state crime" and said that the military shared responsibility, either directly or through negligence.
One theory that it put forward was that cartel members targeted the students because they had unknowingly taken a bus with drugs hidden inside.
President Andres Manuel Lopez Obrador has promised full access to information related to the case.
Former attorney general Jesus Murillo Karam, who led a controversial investigation into the mass disappearance, was arrested last year on charges of forced disappearance, torture and obstruction of justice.
He is considered the architect of the so-called "historical truth" version of events -- presented in 2015 by the government of then-president Enrique Pena Nieto -- that was widely rejected, including by relatives.
In June, eight soldiers were detained for the alleged crime of forced disappearance.
So far the remains of only three victims have been identified.