Cesar Nava Gonzalez was arrested on November 16, the statement said yesterday, calling the former official a "member of the Guerreros Unidos criminal organization."
The teacher college students' disappearance and presumed slaughter has infuriated Mexicans fed up with corruption, impunity and a drug war that has left more than 100,000 people dead or missing since 2006.
Lawyer Vidulfo Rosales, who represents the parents of the missing students, said the families were told yesterday of the latest arrest at a briefing with officials.
Members of the Guerreros Unidos drug gang have told investigators they killed the students and burned the bodies after police had handed them over.
The then police chief Nava Gonzales, who had been on the run since soon after the crime came to light, has confessed to responding to a call from the Iguala police chief on the night of September 26, to help with detaining the students, said lawyer Rosales.
Iguala's police chief remains at large, but the Iguala mayor and his wife have both been arrested.
Prosecutors accuse the mayoral couple of colluding with the gang and ordering the attack over fears the students would disrupt a speech by the mayor's wife, who was head of the local child protection agency.
Officials have stopped short of declaring the students dead, pending an Austrian university's DNA tests on charred bones. Federal authorities continue to search for them in Guerrero.
