An Argentine court has sentenced Reynaldo Bignone, the country's last dictator, to 20 years in prison for his part in Operation Condor.

It's the "first time a court has ruled that Operation Condor was a criminal conspiracy to kidnap and forcibly disappear people across international borders," The Associated Press reports.

Under this plan, the military dictatorships in Argentina, Chile, Paraguay, Bolivia, Uruguay and Brazil agreed to share information with each other to help track down political opponents and leftists starting in 1975. 376 people were killed as a result of Operation Condor, the BBC reports. As The Guardian describes, "after their arrest, the victims were made to 'disappear', usually by being cremated, or thrown drugged but still alive from military planes into the Atlantic Ocean."

This trial was looking into 105 of those cases, Reuters reports.

Additionally, the AP reports that "various U.S. government agencies were aware of the plan," citing declassified documents.

The Argentine federal court also handed prison sentences to 14 former military officers. Bignone, who ruled Argentina from 1982-83, was found guilty of "being part of an illicit association, kidnapping and abusing his powers in the forced disappearance of more than 100 people," the AP reports.

88-year-old Bignone is already serving prison time for multiple convictions of crimes against humanity.

Human rights groups view this as a landmark ruling.

"This ruling, about the coordination of military dictatorships in the Americas to commit atrocities, sets a powerful precedent to ensure that these grave human rights violations do not ever take place again in the region," Jose Miguel Vivanco, Americas director for Human Rights Watch, told Reuters.

"This is a great ruling, with stiff sentences," Luz Zaldua, a lawyer representing victim's families, told the AP. "It has established that Condor was a supranational criminal association, and that's important - not just for our country but for all countries that have been part of this operation."

As Reuters explains, previous cases have focused on individual crimes that occurred during Operation Condor, but this is the first time a court has focused on "participation in the plan itself."

The courtroom Friday was "packed with victims' relatives, who sat in stony silence during the lengthy reading" of the sentences, The Guardian reports.

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