The Spanish Supreme Court has quashed an al-Qaeda suspect's conviction for helping plan the 11 September attacks.
Yarkas allegedly became an al-Qaeda cell boss in 1995
The court overturned a 15-year jail term given to Syrian-born Imad Yarkas, but upheld a 12-year sentence for belonging to a terrorist group.
Three other suspects were acquitted over alleged links to a terror group.
Yarkas, also known as Abu Dahdah, was arrested in November 2001, about four years after Spanish police began tapping his telephone.
He is believed to have led a Spanish al-Qaeda cell since 1995.
The three men acquitted by the tribunal - Moroccans Driss Chebli, Sadik Merizak and Abdelaziz Benyaich - were released in April at the request of prosecutors.
The reasons behind the verdicts published on Thursday are due to be given at a later date.
Yarkas was jailed in September last year along with 17 other men convicted on charges of aiding al-Qaeda.
At the trial, prosecutors called for him to be jailed for 25 years for each of the 2,973 people killed in the 2001 attacks.
But earlier this year they asked for his conviction to be overturned because of lack of evidence.