Political leaders greeted the news with relief and joy, and hailed the persistence of anti-Eta peace movements who mobilised ever larger demonstrations in Mr Aldaya's support several times a week since his kidnap last May. None the less, the decision to free him was Eta's own, taken after the organisation had received up to 150m pesetas (pounds 750,000) ransom from the industrialist's family, and owed nothing to either mass demonstrations or police manhunts.
"It was unfortunate," remarked Jose Maria Aznar, the leader of the conservative Popular Party, who is due to form the new Spanish government, "that Mr Aldaya's freedom was consequence of a decision of his captors and not achieved through the actions of the security forces."
Mr Aldaya was freed in wooded hills near the Basque town of Elgoibar in the early hours of yesterday and made his way to a restaurant where he telephoned the police and his family. A spokesman said he was in good physical and mental shape, and that he would give a full account of his ordeal tomorrow.
Security officials believe Mr Aldaya's seizure and long detention was orchestrated by a special Eta kidnap squad that operated separately from other Eta commands. This squad remains intact, despite mammoth police operations in recent months and well-trumpeted detentions of Eta suspects and seizures of arms caches.
Mr Aldaya, 54, whose transport company is based near the Basque city of San Sebastian, is a prosperous businessman but far from a financial mogul. His family said Eta's ransom demands far exceeded their means, and this is thought to have been the main obstacle to obtaining his earlier release.
The operation marks not only a logistical coup for Eta, but also a financial one. The Interior Ministry suspect that fear among Basque entrepreneurs caused by the kidnapping prompted a flow of contributions to Eta's coffers by those eager to avoid a similar fate.
Eta still holds Jose Antonio Ortega Lara, a prison officer from the Basque town of Logrono captured in January. The organisation says it will release him only when the government agrees to return more than 500 Eta prisoners dispersed around Spain to prisons nearer their homes.