The Federal Court in Argentina has released 10 army officers accused of executing 22 prisoners almost two decades ago.
The new president has repealed laws protecting old regime members
The officers were arrested and indicted earlier this month for the killings, which took place shortly after a coup that ushered in a six-year military dictatorship.
Lawyers for the victims families say the officers were freed on a legal technicality.
The execution of the prisoners on the 13 December 1976 has become known as the Margarita Belen massacre.
It was one of the most notorious human rights abuses committed by Argentina's military dictatorship, which had come to power earlier that year.
So when 10 officers were arrested and indicted for the killings just three weeks ago, human rights organisations hailed it as a big step for justice.
But now, the federal court in Chaco province - where the executions took place - has freed them.
It ruled that it had no jurisdiction over the case.
Impunity 'not over'
However, it is not clear why jurisdiction is an issue. Mario Bosch, a lawyer for the victims families, has promised to appeal against the ruling.
He says two of the federal court judges who made the decision served under the old military dictatorship, and they have an obvious conflict of interest.
Up to 30,000 people were killed or disappeared in the Argentine military's campaign in the 1970s against what it called left-wing insurgents, in what was called the Dirty War.
Argentina's new president, Nestor Kirchner, opened the way for prosecutions like this when he repealed amnesty laws that protected members of the old regime.
Human rights groups say the latest release demonstrates that the fight against impunity still is not over.