Mounir al-Motassadek was the only person in the world convicted in connection with the 11 September 2001 attacks in the United States. But in March 2004, Germany's Federal Criminal Court quashed his conviction, setting the way for a retrial beginning five months later.
Motassadek's conviction was thrown out due to doubts about evidence
BBC News Online explains how the current situation came about and what the possible consequences could be.
Q: What exactly was Mr Motassadek convicted of?
Mr Motassadek was convicted of being an accessory to more than 3,000 counts of murder. He was found guilty of helping the other 11 September plotters who were based in Hamburg, providing them with logistical support and other aid.
He was the only man in the world to be convicted in connection with 9/11.
Q: Why was his conviction struck down?
His conviction was put in doubt following the February 2004 acquittal of another Moroccan man, Abdelghani Mzoudi, on the same charges. His lawyers argue key evidence provided by Ramzi Binalshibh would exonerate him.
Q: What is the role of Ramzi Binalshibh's evidence in all this?
Mr Binalshibh was also allegedly a member of the Hamburg cell. He was arrested in Pakistan a year after the attacks, and is now in US custody. He allegedly told US interrogators the cell consisted only of himself and three suicide hijackers, including Mohammed Atta - so by implication Mr Motassadek and Mr Mzoudi were not guilty.
Prosecutors believe, however, that the full transcript of Mr Binalshibh's interrogation would put it in a different light and allow them to secure the conviction of both Moroccans.
Q: How can Mr Binalshibh's evidence be seen as reliable?
Good question. The point the court made in the Mzoudi trial was that because it was unable to cross-examine Mr Binalshibh, it could not determine whether or not he is reliable.
So the defendant must get the benefit of the doubt.
Is a retrial likely to produce a different result from the original trial?
Possibly not. The prosecution had urged US intelligence agencies to make more information public so it can be used against Mr Motassadek.
But as the new trial was opening the US Justice Department announced that it would not allow al-Qaeda suspects in US custody to testify.
Also, in the wake of the Abu Ghraib prisoner abuse scandal, the defence is set to argue that any information from the US is suspect because it may have been obtained through torture.
Q: What are the implications for the international fight against terrorism and for trials related to the 11 September attacks?
The whole thing is an embarrassing setback for the German efforts to fight terrorism in the courts. It points to how complex it is to prove in a court of law that someone took part in acts of terrorism.