The arrested said they took the students to a garbage dump in Cocula, where they were executed and incinerated. Their ashes were then thrown into the San Juan Cocula River.

Parents of the missing have been demanding the government continue to search for the students whose remains have not been identified and investigate the army's role in the incident.

The attorney general said, however, "there isn't a single piece of evidence" that the army had a role in the killing.

The fact that the remains of one student, Alexander Mora Venancio, were identified has also proved the authorities' judgement, while experts in Austria are still working to identify the remaining victims, Murillo added.

According to the Mexican daily La Jornada, Murillo said the case has to be closed before the authorities can convict and sentence the suspects in custody, even though other suspects have yet to be seized.

The mayor of Iguala, who allegedly had ordered the killings, and his wife are among the 99 people arrested so far in connection with the crime.