MEXICO CITY (AP) — Mexico said Monday it has arrested the former head of a federal anti-kidnapping unit in connection with the disappearance of 43 students in 2014.

Gualberto Ramírez was head of the anti-kidnapping unit for the attorney general’s office when the students from the Ayotzinapa teachers college in southern Mexico went missing.

Assistant Interior Secretary Alejandro Encinas wrote that Ramírez faces charges of disappearance, torture and conspiracy for the botched investigation into the abductions, which are defined as “disappearances” under Mexican law because only remains of three of the victims have been identified.

Security forces abducted the students from buses in the city of Iguala on Sept. 26, 2014, and turned them over to a local drug gang, which apparently killed and burned them.

A Mexican military official confirmed last week that eight soldiers have been detained in the case and are awaiting the possible filing of charges by civilian prosecutors.

Recent revelations implicate the military in the disappearances, but the motive for the students’ abduction remains unclear, though there is growing evidence it may have involved police and military collusion with drug traffickers.