Six years after 43 students disappeared and were most likely murdered in south-western Mexico, arrest warrants have been issued for several suspected soldiers and a federal police officer.
"We must not give up hope," Mexican President Andres Manuel Lopez Obrador said on Saturday. "There will be justice."
The government has promised further investigations.
The 43 young men were studying in a rural teacher training college in Ayotzinapa and went missing in the city of Iguala when travelling in buses they had stolen on September 26, 2014.
They were pursued by police and allegedly handed over to the crime syndicate Guerreros Unidos, for reasons that are not known.
An earlier investigation said the bodies of the young people had been burned at a rubbish dump, but that version of events was later discredited.
So far, only the bones of two victims have been found. The details and background of the crime are still unclear. To date, no one has been convicted.
Lopez Obrador's government relaunched the investigation after the previous one was plagued with irregularities and more than half of 140 suspects were released.
"There will be no impunity," said Alejandro Encinas, secretary of state for Human Rights in the Ministry of Interior. "Those responsible will be brought to justice."
On Saturday in Mexico City, demonstrators marched from the Independence Monument to the central Zocalo Square in memory of the abductees.
They chanted: "You took them alive, we want them back alive" and sprayed slogans and the number 43 on the facade of the National Palace.
Relatives of the victims had erected a "wall of remembrance" in front of the Attorney General's Office in the city on Friday, showing photos of the missing persons.
The UN High Commissioner for Human Rights acknowledged progress in the investigation, but also called on authorities to redouble their efforts.
Recently, several suspects were released because they had been tortured while in custody.
In Mexico, over 73,000 people are considered to be missing. In the search for abducted students alone, 245 bodies of other murder victims were discovered around the city of Iguala in Guerrero. Only 22 have been identified so far.
Australian Associated Press
