A federal court in Mexico has suspended the trial on genocide charges of the former President, Luis Echeverria.
Mr Echeverria was interior minister at the time of the 1968 killings
He is alleged to have had a role in the killing of dozens of students during a demonstration in Mexico City in 1968.
The ex-president's lawyer said the ruling indicated there was no evidence to link Mr Echeverria to the deaths.
Mr Echeverria, who was interior minister at the time, has repeatedly denied any role in the deaths. The prosecution has 10 days to appeal.
Juan Velazquez, Mr Echevarria's lawyer told the BBC he was confident the prosecutors would accept the court's ruling, bringing the trial to an end.
Human rights groups say as many as 300 student activists were killed when troops opened fire on them in Mexico City's Tlatelolco Plaza on 2 October, just days before the city hosted the Olympic Games.
Official reports put the death toll at 25.
Mr Echeverria has repeatedly denied allegations that he gave orders for soldiers in the plaza to open fire on the anti-government protesters.
He has also disputed that the deaths constituted genocide.
Mr Echeverria was president from 1970 to 1976 during which hundreds of people died or disappeared during a campaign against leftists called the "dirty war".
The 84-year-old former president, who was placed under house arrest in November last year, is in poor health.