The head of Mexico's criminal investigation agency, charged with looking into the disappearance of 43 college students, has resigned.
The families of the students, who have not been seen since September 2014, had demanded that Tomas Zeron resign.
No reason was given for him standing down on Wednesday.
Families have disputed the government's official version of events, which said the students were killed and incinerated at a dump site.
The government had said that the students were arrested by municipal police on 26 September 2014 in the town of Iguala, in Guerrero state.
The prosecutor general at the time, Jesus Murillo Karam, said the police had handed the students over to a drug trafficking gang, who had killed them at the rubbish dump and then built a large funeral pyre with the bodies to burn them.
Two independent international investigations have since dismissed those initial claims, and the families of the missing had asked that other avenues be explored.
Mr Zeron oversaw investigators as well as the forensic work of the criminal investigation agency.
However his own handling of a crime scene was placed under investigation in April following criticism from the Inter-American Commission on Human Rights.
It emerged he had visited the fire scene a day before evidence was found, along with one of the alleged gang members, without noting the visit in official records.
Relatives of the missing college students said they would hold a press conference on Mr Zeron's departure on Thursday.