Reed Brody: Historic moment in the fight to ensure there are no safe havens for mass killers

The extradition of Ricardo Miguel Cavallo from his hiding place in Mexico to Spain for alleged crimes committed during Argentina's "dirty war" marks a historic moment in the effort to bring to justice the perpetrators of the worst atrocities.

Cavallo's transfer is the first time that one country has extradited a person to another country to stand trial for abuses that happened in a third.

Argentinian victims, like the Chilean victims of General Augusto Pinochet, sought justice in Spain after the courthouse doors in their home countries were shut in their face by amnesty laws. Spain indicted Cavallo, as it indicted Pinochet, under the principle of "universal jurisdiction": the rule that every state has an interest in bringing to justice the perpetrators of the worst international crimes, no matter where the crime was committed, and regardless of the nationality of the perpetrators or victims.

Universal jurisdiction has been incorporated into a number of treaties seeking to make sure that there is no "safe haven" for those responsible for the most serious crimes.

Since the end of the Second World War, the list of crimes giving rise to universal jurisdiction under international law has grown to include genocide, torture, war crimes, apartheid and other crimes against humanity.

In the landmark Filartiga case, in which the family of a Paraguayan torture victim living in the United States sued his torturer, who had moved to New York, a US court said: "The torturer has become, like the pirate and slave trader before him, hostis humanis generis, an enemy of all mankind."

Universal jurisdiction by national courts complements the role of the new International Criminal Court, whose jurisdiction is not retroactive and which covers only crimes committed on the territory of the 90 states that have ratified the ICC treaty, or by their nationals.

Ironically, the Cavallo extradition comes at a time when the principle of universal jurisdiction is under attack from the United States. The Pentagon apparently wants to immunise itself from any legal restraint on its conduct by barring even the theoretical possibility that top US officials could be judged by the ICC or the courts of another state.

It used to be said: "Kill one person and you go to jail, kill 20 and go to an insane asylum, kill 20,000 and grant yourself an amnesty." The principle of universal jurisdiction says that your amnesty may not be valid in other countries. The Cavallo extradition says that you can run but you cannot hide.

Reed Brody is special counsel with Human Rights Watch. He participated in the House of Lords proceedings in the Pinochet case and leads the group's campaign to bring to justice perpetrators of atrocities.