Fears grow that the first conviction for September 11 attacks will be the last

Mounir al-Motassadeq may be the first man to be convicted in connection with the 11 September attacks on America, but as prosecutors around the world endure the frustrations of elusive or missing evidence and the reticence of national security agencies with valuable information to offer, there are doubts whether there will ever be a second.

The verdict of the Hamburg court, which found Motassadeq guilty as an accessory to mass murder, was itself a close-run thing. Defence lawyers sought to depict the evidence against him as no more than a web of suppositions based on his unfortunate choice of friends – Mohamed Atta, Ziad Jarrah, Marwan al-Shehhi and other people involved in the attacks.

Even the judge, Albrecht Mentz, intimated towards the end of the three-month trial that the court might want to consider lesser charges – although he changed his mind. And there may yet be some kind of reversal on appeal.

Prosecutors in Germany, the United States and elsewhere have several problems. The hijackers themselves are dead, some of the other main suspects remain at large, and some of the best evidence – from captured senior al-Qa'ida operatives and plotters – is being guarded for security reasons.

Motassadeq was convicted over evidence that he and his lawyers found impossible to explain. He had power of attorney over the bank account of Shehhi, one of the pilots of the hijacked planes, and according to prosecutors organised many of the money transfers that financed the attacks.

He also admitted training at an al-Qa'ida camp in Afghanistan, lived for a time in the flat used as the headquarters of the so-called Hamburg cell, and was a signatory to Atta's will – suggesting, as the judge put it, that he was part of the plot "from its inception".

The biggest flaw in the case, one that may lead to an appeal, was the defence's unfulfilled request to call two witnesses: Motassadeq's one-time room-mate, Ramzi bin al-Shibh, who investigators believe intended to be the 20th hijacker but who failed to obtain a US visa, and Mohammed Haydar Zammar, an alleged al-Qa'ida recruiter in Hamburg now in jail in Syria.

Mr Shibh has been in US custody since his capture in Pakistan last October. The Americans refused to make him available in the Motassadeq case, and are fighting to keep him out of the US case against Zacarias Moussaoui, the Frenchman arrested three weeks before 11 September.

There is some debate whether the US line in the Moussaoui case is dictated by security concerns, or whether John Ashcroft, the Attorney General, is afraid Mr Shibh's testimony might scupper his ambitions to have Mr Moussaoui sentenced to death. Evidence now suggests Mr Moussaoui was never a serious candidate for participation in the attacks because the plotters thought he was too unstable.