The parents of 43 Mexican students who disappeared from the town of Iguala in 2014 have condemned an order to release 24 suspects in the case.
A judge ordered that 24 local police officers arrested in connection with the students' disappearance should be freed immediately.
The judge said they had been tortured while in custody and should go free.
A Mexican government official accused the judge of using "questionable criteria" to reach his decision.
The judge's decision came just days after another key suspect in the case was released.
Gildardo Lopez Astudillo was suspected of being the gang leader who ordered the killing of the students. He too was released after it was found that he had been tortured.
What is the case about?
The case dates back to 26 September 2014 when 43 students from a teacher training college in the town of Ayotzinapa in Guerrero state disappeared after attending a protest in the nearby town of Iguala.
They were part of a larger group and, as they were travelling back from Iguala to Ayotzinapa, they were confronted by municipal police, who opened fire on the buses they were travelling in.
The officers maintained they had done so because the buses had been hijacked, while the surviving students said the drivers had agreed to give them a lift.
During the clash, five people - two of them students - were shot dead. The body of a third student was found mutilated near the scene of the clash the next morning.
Forty-three of the students vanished after the clash. An official government report said they had been seized by the municipal police officers who handed them over to a local drugs gang.
The report concluded that the drugs gang had killed the 43, burned their bodies and dumped the ashes in a local stream.
However, independent investigators have described the official investigation as "deeply flawed" and human rights groups say some of those arrested were tortured to make them confess.
On Saturday, the attorney general's office said it would investigate officials who had handled the investigation so that the officials "who had failed in their duties" could be held accountable.
What did the judge order?
Judge Samuel Ventura ordered the immediate release of 23 men and one woman - all of them police officers in Iguala and nearby towns - accused of organised crime and forced disappearance.
He said that the suspects had been tortured to force them into confessing and there was insufficient evidence to continue to hold them.
However, eight of the suspects still have other cases pending and will remain in custody.
What was the reaction?
Deputy Secretary of Human Rights Alejandro Encinas said the order to release the 24 police officers was an "affront to the victims" which "made a mockery of justice" in Mexico.
He said that of 142 people detained in connection with the case, only 65 remained in custody.
Melitón Ortega, the father of one of the missing students, said the judge's decision was a blow to the parents and that it constituted a setback in their efforts to investigate what had happened on the night of the students' disappearance.
"Those freed have very valuable information that will now not come to light. We're not advancing as we'd like to, it's all going very slowly but we're going to keep the pressure up," Mr Ortega said.