Mexico has handed human rights groups a major victory in what has been a long - and, until now, losing - battle for "universal jurisdiction," the principle that gross rights violations may be tried by courts outside the country where the crime took place.
Last week, the Supreme Court here upheld a ruling to extradite a former Argentine military official wanted in Spain for alleged atrocities he committed in Argentina in the 1970s and 1980s.
Ricardo Miguel Cavallo faces prosecution for murders and abductions that took place when he was a Navy lieutenant in Buenos Aires, and worked in the Navy Mechanical School, one of the most notorious centers of repression during Argentina's so-called Dirty War. He will be sent to Spain in the next week.
"This will be the first time that one country extradites a person to another to stand crimes for something that happened in a third," says Reed Brody, a prosecutor at Human Rights Watch and an expert on universal jurisdiction.
Human rights activists the world over have been generally frustrated in efforts to extradite former officials wanted for gross violations during their rule.
Back in 1999, former Chilean dictator Augusto Pinochet sat in a London jail for 18 months as Spain fought unsuccessfully to extradite him for the alleged death or disappearance of 4,000 people during his reign. He was eventually sent back to Chile but never faced trial because of poor health.
Idi Amin, the Ugandan leader whose reign of terror left more than 100,000 people dead, now lives comfortably in Saudi Arabia, which has resisted efforts to bring him to justice. And efforts to extradite two former Haitians - military ruler Raul Cedras, who lives in Panama, and former paramilitary leader Emmanuel "Toto" Constant, who resides in New York - have failed.
"With all of the legal and human rights advances of the 20th century, immunity for mass atrocities is still the norm," says Mr. Brody.
Critics of universal jurisdiction say it goes against the idea of national sovereignty and puts world leaders at the whims of foreign courts.
But some legal experts say the principle of universal jurisdiction exists precisely because most governments do a poor job of investigating abuses by their predecessors, usually for political reasons. They say it's important that Mexico backed the Cavallo extradition, since it indicates a greater support for human rights principles than past governments in Mexico and across Latin America have generally shown.
Legal efforts to prosecute former Latin American officials wanted for war crimes have had little success. In El Salvador and Argentina, for example, subsequent governments simply granted amnesty to most of the officials accused of atrocities, or handed out post-conviction pardons. Here in Mexico, efforts to investigate the past have bogged down.
"Our own courts are very slow, very delayed in dealing with Mexico's history of injustice," says historian Enrique Condes Lara, who investigates Mexico's own Dirty War era.
During the late 1970s and early 1980s, hundreds of leftists - many of them students - disappeared and were presumed killed. Thousands more were jailed and tortured.
Victims, their families, and rights groups have long demanded accountability and justice for the perpetrators. To this day, only one ex-president, Luis Echeverría, has had to answer charges that he played a major role in two student massacres. He has since avoided a trial, with his lawyers also citing his advanced years and poor health.
Cavallo's accusers say he belonged to the operations sector of Working Group 3.3.2, a unit involved in kidnapping and torturing persons perceived to be leftist by the military. More than 9,000 Argentines vanished during their country's military regime. Most are presumed dead.
Cavallo has admitted he was a member of Argentina's military during that era, but denies he engaged in torture. He was found in Mexico almost three years ago, where he had lived quietly, running this country's motor-vehicle registry, until an unrelated controversy put his face in the news and five former political prisoners identified him as their torturer from 1976 to 1983.
After a lengthy appeal, the Mexican Supreme Court authorized Cavallo's extradition on charges of genocide and terrorism, but not on charges of torture. A lower court had previously ruled that Cavallo could not be extradited for torture on the grounds that, under Mexican law, the statute of limitations for a torture prosecution had already expired.
"We are sorry the torture charge was left out," says Irma Pérez-Gil de Hoyos, a prominent rights activist in Mexico, "but it still marks a big step forward in the fight against the impunity and against various types of genocide in the world."