Spain has ruled against trying former Argentine junta officer Ricardo Cavallo on human rights charges but invited Argentina to call for his extradition.
Ricardo Cavallo has been in custody in Madrid since June 2003
The high court in Madrid decided it had no jurisdiction over Mr Cavallo, who has been in Spanish custody since 2003.
Argentina has not yet commented. The ex-naval commander is facing genocide and terrorism charges, 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.
Ricardo 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.
Mr Cavallo was extradited to Spain from Mexico in June 2003, and Spanish prosecutors had requested up to 17,000 years in prison 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However, Argentina's Supreme Court repealed the laws in 2005, paving the way for possible criminal proceedings.
Under the Spanish ruling Argentine authorities have 40 days to request Mr Cavallo's extradition.
Spain has been investigating violations by former military regimes in Argentina and Chile for more than a decade under a legal doctrine that allows prosecution of crimes like terrorism even if they are alleged to have been committed elsewhere.
In April 2005, another former military officer from Argentina, Adolfo Scilingo, was sentenced in Spain to 640 years in prison for crimes against humanity.