The Supreme Court threw out a 1989 presidential pardon that absolved a former army general of alleged human rights abuses during Argentina's dictatorship.
Friday's ruling that the pardon of General Santiago Omar Riveros was unconstitutional opens the door for lower courts to reconsider dozens of other pardons granted after the end of the 1976 to 1983 military regime.
The court's seven members voted 4 to 2, with one abstention, that Riveros can be tried for illegal abductions, torture and killings of dissidents during a crackdown known as the Dirty War.
Nearly 13,000 people are officially reported as missing from the junta era, though human rights groups say the toll is closer to 30,000 victims.
President Nestor Kirchner has made settling dictatorship-era human rights cases a priority. Since 2005, when the Supreme Court struck down 1980s laws granting blanket amnesty to people involved in official repression, dozens of former military and police officers have been called before the courts.
Last year, former police investigator Miguel Etchecolatz was convicted of genocide and sentenced to life imprisonment. That trial was marred by the disappearance of the chief prosecution witness, torture survivor Jorge Julio Lopez, who remains missing.
A high-ranking commander during the junta, Riveros was known for his harsh direction of one of the army's torture centers, Campo de Mayo.
He was accused in connection with 14 killings and 20 cases of torture at army institutes under his command, before being pardoned by then-President Carlos Menem.
Riveros has been under house arrest since 2000 as part of a trial of military officials who allegedly arranged the illegal adoption of more than 200 children born in detention centers. Charges of child kidnapping never went to court and were not covered by the presidential pardon.
Menem issued a statement on Friday defending his pardons and accusing Kirchner of a "vendetta" against former members of the military while not lifting pardons granted to leftist "terrorist organizations" they sought to crush.
Menem is making a long-shot bid to regain the Argentine presidency in October's election. The race's front-runner is Kirchner's wife, Senator Cristina Fernandez de Kirchner.
Argentine constitutional scholar Gregorio Badeni noted that during the 1990s, the Supreme Court -- dominated by Menem appointees -- had ruled that the Riveros pardon was valid.
"I don't really understand the court's argument for going against its earlier ruling," he said.
The Supreme Court said in a statement that the alleged crimes violated not only Argentina's constitution but also international law and treaties still in effect.