The Spanish high court imprisoned an al-Qaeda leader for 27 years today after finding him guilty of conspiring with the team of hijackers that committed the September 11 attacks.

But the sentence, which came at the climax of the trial of 24 alleged al-Qaeda operatives in Madrid, was a mixed success for prosecutors. Three senior Spanish judges cleared Imad Yarkas of being an accomplice to murder, the most serious charge against him.

Yarkas and two other defendants, Driss Chebli and Ghasoub al Abrash Ghalyoun, were accused of conspiring to commit 2,973 murders on September 11, and faced prison sentences of 74,000 years each, but they were acquitted of those charges for lack of evidence.

Instead, Yarkas was jailed for 27 years on conspiracy charges and for heading a terrorist organization; Chebli was convicted for collaborating with a terrorist organization; and Ghalyoun was cleared of all charges. Of the remaining 21 people on trial, 16 were convicted for a range of terrorist-related offences, although none relating to 9/11.

The central accusation against Yarkas, who is Spanish but of Syrian origin, was that he organised a meeting in Spain in July 2001 at which Mohamed Atta and fellow hijacker Ramzi Binsalshibh met to decide last minute details, including the date of the 9/11 attacks.

Ghalyoun, who is also Syrian-born, was accused on the basis of video footage he shot of New York's landmarks while he was on holiday in the city. All charges against him were thrown out. "The lack of evidence to show the three suspects took part in such despicable murders, either as material participants... or as accomplices or harborers, is absolute," said the court's judgement.

Today's sentences, which ranged from six years to Yarkas's twenty-seven, came at the end of the longest and most elaborate of Europe's terrorism trials. Over 100 witnesses were called to give evidence during two-and-a-half months of proceedings in a special high-security courtroom on the outskirts of Madrid.

At his sentencing, Yarkas became the only person in the world with a standing conviction after being tried over 9/11.

In Germany, Mounir el Motassadeq was convicted in 2003 but acquitted last month in a retrial, although he was found guilty of belonging to a terrorist cell. The only person charged in America over September 11 is Zacarias Moussauoi, who pleaded guilty to being the twentieth hijacker in April but is yet to be sentenced.

Among those convicted today was Tayseer Alouni, a journalist for al-Jazeera, who was sentenced to seven years for collaborating with a terrorist group.

The Qatar-based satellite broadcaster denounced the sentencing of Alouni, who became well-known throughout the Arab world as the Kabul correspondent for al-Jazeera during the US-led invasion of Afghanistan in October 2001. Alouni interviewed Osama bin Laden shortly after the September 11 attacks.

"We were all shocked because everyone expected Alouni to be freed. It is a regrettable event in the history of international journalism when a journalist who sought the truth becomes the accused," said Ahmed al-Sheikh, the al-Jazeera news editor.

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