The Supreme Court in Spain has ruled that a former Argentine junta officer should stand trial in Madrid for crimes against humanity.
Ricardo Cavallo has been held in a Spanish prison since 2003
The decision annuls an earlier ruling by the High Court that Ricardo Cavallo should face justice in Argentina.
Prosecutors argued that the case in Spain was in a more advanced stage than the one against him in Argentina.
Mr Cavallo is accused of killing and torturing left-wing activists in the so-called dirty war of the 70s and 80s.
He was extradited to Spain from Mexico in 2003, where he had lived for years under an assumed name.
Spanish law allows offences committed abroad to be tried in Spain if a suspect is not facing prosecution in his home country.
The ex-naval commander has been charged by Spanish authorities with genocide and terrorism, which he denies.
Up to 30,000 people are said to have been killed or disappeared in Argentina during the "dirty war" of 1976-1983.
Mr Cavallo served at the notorious Navy School of Mechanics in Buenos Aires, a detention centre in which hundreds of people were tortured and killed.
At least 614 people were held at the navy school during the military campaign against left-wing insurgents. Many were drugged and thrown from aircraft into rivers and the sea.
Spanish prosecutors have requested multiple life sentences in prison for Mr Cavallo, for the death and torture of Spanish citizens.
Military officers who carried out the human rights abuses were granted immunity from prosecution in Argentina under laws passed soon after the return to democracy.
However, Argentina's Supreme Court repealed the laws in 2005, paving the way for possible criminal proceedings.