Federal police in Mexico have arrested a man they say is a key suspect in the disappearance of 43 students from the town of Iguala in 2014.
Erick Uriel Sandoval is accused of forming part of the gang that is thought to have killed the trainee teachers and burned their bodies.
He was arrested in Cocula, the town near the rubbish dump where remains of one of the missing students were found.
The disappearance of the 43 caused outrage in Mexico and abroad.
Alfredo Higuera from the prosecutor's office in charge of investigating the case said that Mr Sandoval was accused of having "played a key role in the actions against the students".
Local media alleged that he was one of the gang members tasked with shooting dead the students.
Vanished after protesting
The 43 were part of a larger group of students from a teacher training college in Ayotzinapa who travelled to the nearby town of Iguala to protest against what they saw as discriminatory hiring practices for teachers.
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 did so because the buses had been hijacked, while the surviving students said that the drivers had agreed to give them a lift.
The 43 missing students have not been seen since that clash on 26 September 2014.
According to the official government report, they were handed over by corrupt police officers to members of local drugs gang Guerreros Unidos (United Warriors).
The gang then took them to a local rubbish dump, where they killed them and burned their bodies, the official report continues.
However, independent experts have cast doubt on the official report, pointing out that the chain of evidence was broken when the bone fragments were tested.
They also said that the government had hampered their investigation.
Mr Sandoval is accused of forming part of the Guerreros Unidos drugs gang and prosecutors say he had "direct contact" with the students following their disappearance.
He is one of five suspects for whom prosecutors have offered a reward of 1.5m pesos ($81,000; £58,000).
One of the members of Guerreros Unidos already in custody has reportedly named Mr Sandoval as one of the people who were at the rubbish dump the night the students were killed and their bodies burned.
More than 100 people have been arrested in connection with the case but, two and a half years since the students' disappearance, doubts remain as to what happened to them.