The case was opened in the Spanish national security court, the Audencia Nacional. In July 2006, the Spanish Supreme Court overturned the conviction of a former Spanish citizen who had been held in Guantánamo, labeling the regime established in Guantánamo a “legal black hole.” The court forbade Spanish cooperation with U.S. authorities in connection with the Guantánamo facility. The current criminal case evolved out of an investigation into allegations, sustained by Spain’s Supreme Court, that the Spanish citizen had been tortured in Guantánamo.
The action was taken by Judge Baltasar Garzón, referred to as "Europe's counter-terrorism magistrate."
Garzón is best known for his prosecution of a criminal investigation against Chilean dictator Augusto Pinochet that resulted in the issuance of an arrest warrant for Pinochet while he was visiting England.
The action means that if these lawyers travel to Spain or to the 24 countries that participate in the European extraditions convention outside the U.S., they could be arrested. They could also be arrested in other countries, but that would require more extensive extradition proceedings.
Update: Rough translation from El Pais:
The judge, has reopened the case, saved since March 2008, and has been transferred to the prosecutor of the Audiencia Nacional to inquire about whether to admit the criminal complaint filed against the six lawyers who participated in the preparation, approval and implementation of the legal framework in Guantanamo.
This lawsuit was filed by the Association for the dignity of prisoners, reports the SER for the purpose of investigating a crime against the international community to this group of lawyers working for Undersecretary of Defense for the Attorney General or as advisers to George Bush.
AFP article here.
Spain operates under the principle of "universal jurisdiction," a doctrine that allows courts to reach beyond national borders in cases of torture, terrorism or war crimes.
Much more here.
The case was not formally accepted by the court yet, but Baltasar Garzon has ordered the prosecution to start a criminal probe against the six.
The Publico article is here and El Pais' article is here. The Publico article, translated, says:
The document [complaint], of almost 100 pages, constitutes an exhaustive chronicle of how the Administration of Bush assembled a new legal corpus that threw for the gunwale all a legalistic tradition of more than 200 years. The documents show that the advisors of Bush knew the international law and they violated it consciously, according to the plaintiffs.