In August, 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.
The Interdisciplinary Group of Independent Experts (GIEI) questioned the credibility of purported WhatsApp messages presented by the commission as apparent evidence of collusion between criminals and authorities.
“It’s not possible to guarantee the authenticity of the messages,” which were shared as screen shots, a member of the group, Francisco Cox, told reporters.
The GIEI, created in 2014 under an agreement between Mexico and the Inter-American Commission on Human Rights, expressed concern that the government was trying “to speed up the results” without a full investigation.
The experts noted that some of the messages purportedly sent before the students disappeared had two blue ticks indicating they had been read — a feature only later introduced by WhatsApp.
Last week, the truth commission’s head, deputy interior minister Alejandro Encinas, said that of 154 screen shots, 99 were consistent with other evidence and 55 were not.
The teaching students had commandeered buses in the southern state of Guerrero to travel to a demonstration in Mexico City before they went missing.
Investigators believe that they were detained by corrupt police and handed over to a drug cartel that mistook them for members of a rival gang, but exactly what happened to them is unclear.
One theory put forward by the truth commission is that cartel members targeted the students because they had unknowingly taken a bus with drugs hidden inside.
An official report presented in 2015 by the government of then-president Enrique Pena Nieto concluded that cartel members killed the students and incinerated their remains at a garbage dump.
Those findings, which did not attribute any responsibility to members of the armed forces, were rejected by relatives and independent experts.
So far, the remains of only three victims have been identified.
Prosecutors announced in August that arrest warrants had been issued for more than 80 suspects, including military personnel and police officers, but so far only a handful of them have been detained.