Who is Mr Mzoudi?

He was charged with being an accessory to murder and membership of a terrorist organisation, which amounts to a charge of conspiracy in relation to the 9/11 attacks.

The circumstantial evidence against him included the fact that he was a friend and fellow student of the 9/11 attackers, took over the apartment of Mohammed Atta, the lead hijacker, signed his will, attended a terrorist camp in Afghanistan and transferred money for one of the hijackers.

Why was he acquitted?

His trial appeared to be heading for a conviction until a dramatic submission of new evidence in December. A letter passed on to German security services from US officials said that Mr Mzoudi had no prior knowledge of the attacks.

The court said it thought the unnamed source for the letter's claim was Ramzi Binalshibh, the No 4 in the Hamburg cell, who has been in US custody since his arrest in Pakistan on the first anniversary of the attacks.

The letter caused the prosecution's case to crumble, as it could not prove Mr Mzoudi's conspiracy if it could not demonstrate that he knew of the plot in advance.

Judge Klaus Ruehle released Mr Mzoudi immediately as there was no case left for him to answer. Last-ditch attempts by the prosecution to implicate him failed and he was formally acquitted today.

After announcing the verdict, Judge Ruehle told Mr Mzoudi that he had no reason to celebrate. He said that Mr Mzoudi had been acquitted because the evidence had not been sufficient to secure a conviction, not because the court was convinced of his innocence.

What implications does this verdict have?

Mounir el-Motassadeq, who is a friend of Mr Mzoudi, was convicted using very similar circumstantial evidence and given a maximum jail sentence of 15 years in February last year.

At the time the conviction was hailed as setting a precedent, because it was thought that it demonstrated that entire terror networks could be dismantled using these charges. This was significant because many people assist these cells, providing housing, money and all sorts of logistical support.

El-Mossadeq is now appealing against his conviction, and given today's acquittal and the Binalshibh letter, it is likely that the case against him will also unravel. The prosecution in the Mr Mzoudi case will await the appeal verdict, due on March 4, before deciding whether to lodge its own appeal against Mr Mzoudi's acquittal.

Are there any other implications?

The verdict raises the question of whether conspiracy charges can be used to unravel the network that was responsible for the September 11 attacks.

Conspiracy charges are about all that can be used to bring convictions against terrorist networks.

Anti-terror legislation has been tightened and standards of evidence lowered across the world since the attacks, so it should be easier to secure convictions against terrorists and their supporters. But the fact is, after today's acquittal, that even these measures appear not to be enough.

What else do we know of Mr Mzoudi?

He is a Moroccan who was a friend and colleague of the Hamburg cell that plotted the suicide attacks on New York. Along with other members of the Hamburg cell, he was a student of electrical engineering at Hamburg Technical University. He also shared an apartment with them for a time. He is also a devout Muslim and a student of the Koran, having been taken to mosques by his father from the age of five.

What is the reaction to the trial and verdict?

Some of the families of September 11 victims were in court to hear the verdict, and were understandably upset. The German public, which has expected the acquittal since Mr Mzoudi's release in December, is baffled by the verdict. People cannot understand how one terror suspect can be convicted, yet only months later another can be acquitted, when the evidence against both of them is so similar.

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