Mexico's Supreme Court has ruled that a former president accused of human rights abuses can be charged over a massacre of student protesters in 1971.
Luis Echeverria has repeatedly denied any wrongdoing
The court ruled that a 30-year statute of limitations protecting Luis Echeverria from prosecution began only in 1976, when he left office.
The case now returns to a lower court which will have to decide whether there is enough evidence for a trial.
Hundreds died between 1970 and 1976 during a "dirty war" against leftists.
Mr Echeverria, 83, is the first former Mexican president to face the possibility of charges for human rights abuses allegedly committed during his time in power.
Special prosecutor Ignacio Carrillo has accused the former president of ordering men loyal to the government to attack protesters during a student demonstration in June 1971.
Defence lawyers admit that 11 people died in the attack, although Mr Carrillo insists that up to 50 died in the "Corpus Christi massacre".
Mr Echeverria, who was president from 1970 to 1976, has repeatedly denied any involvement in the killings.
He is accused of using a gang of armed government thugs, known as the "Halcones", or Falcons, to systematically attack enemies of the government during his time in office.
Prosecutors have accused 10 other people, including former government members and five members of the Halcones, of involvement in the student deaths.
Earlier this year the Supreme Court ruled that too much time had passed to bring a case against Mr Echeverria.
However, in its latest ruling the court said he received immunity from prosecution while he was in office, and so the 30-year statue of limitations only applied from 1976.