MEXICO CITY (AP) — Mexican authorities arrested the first military officer in connection with the investigation into the 2014 disappearance of 43 students from a teachers' college in southern Mexico.

A federal official who requested anonymity because he was not authorized to speak about the matter confirmed on Friday that Capt. José Martínez Crespo had been arrested.

On the sixth anniversary of the students’ disappearance in September, Mexico’s attorney general said that 25 arrest orders had been issued for suspects in the case, among them soldiers and federal police.

On Sept. 26, 2014, police in the town of Iguala attacked several buses that had been taken by students from the Rural Normal School of Ayotzinapa. The police are believed to have turned over the students to a local drug cartel.

Families of the missing students have long demanded that authorities investigate the possible involvement of the military and federal police.

Clemente Rodriguez, father of student Christian Alonso, who was identified earlier this year through DNA testing of bone fragments, said the arrest of Crespo “is very important for me.”

“Crespo is a key piece,” Rodríguez said. “I hope that he provides information.”

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AP writer Christopher Sherman in Mexico City contributed to this report.