Attorney General Jesus Murillo Karam also said that 14 more local police officers were detained in the case and accused of handing the 43 students over to the Guerreros Unidos gang.
Authorities have found several clandestine graves outside the city of Iguala since the students disappeared after an attack by the gang-connected municipal police, raising fears about their fate.
The first mass grave had five pits containing 28 charred bodies but authorities have not said how many were found in others last week. Another mass grave was found yesterday.
Officials have detained 26 Iguala police officers in the case along with eight other people, including four Guerreros Unidos members.
Also Read
The attorney general announced yesterday that 14 officers from the neighboring town of Cocula were detained.
The officers, he said, took the 43 students from their Iguala colleagues and "then handed them in the city limits of Iguala and Cocula" to the Guerreros Unidos.