At least 25 bodies have been delivered to their families.
The victim filed a criminal complaint in late March, saying she had been unconscious and could not remember the events.
Human rights groups said Cristel Piña, Eduardo Estrada and Leonardo de la O were freed Wednesday.
Sity-one-year-old Esteban Andrés Rodríguez died from the injuries sustained in the incident.
English16/11/2015
Who were the Paris attackers?
The suspected mastermind was already notorious and many of his alleged foot soldiers had crossed authorities' radars.
It has not been fully confirmed that they were pollsters.
Another one of the victims has been released from the hospital.
Peña Nieto reiterated his condolences.
The Executive Committee for the Care of Victims is ready to help the relatives of the students.
English12/09/2015
Three wounded by ray in Veracruz
The victims were taken to a local hospital.