The wife of the former mayor of the Mexican city where 43 students went missing has been charged with organised crime and money laundering.
Prosecutors say Maria de los Angeles Pineda's brothers were in a drug gang that operated in Iguala, Guerrero.
They said police handed the students over to the drug gang after clashes in September. The gang then killed them and burned their bodies.
Maria Pineda and her husband Jose Luis Abarca were arrested in November.
He has been charged with organised crime, kidnapping and murder.
The students' disappearance sparked nationwide protests and has rocked the government of President Enrique Pena Nieto.
Prosecutors said that members of the drug gang linked to Maria Pineda had confessed that her husband, the ex-mayor of Iguala, had ordered the police to crack down on the students to stop them disrupting an event she was speaking at.
However, a local news magazine said the event was over by the time the students arrived in the town.
They vanished after the police attacked their buses, leaving six people dead.
Investigators said members of the drug gang told them the police had delivered the young men to them.
They then took them to a local landfill site, killed them and burned the bodies.
Only one of the students has been positively identified from the charred remains.