The case against the suspected '20th man'

Zacarias Moussaoui always looked like the one who got away. This was a man who, on the morning of 11 September, was seen cheering in front of a television set in the Minnesota jail cell where he was being detained on an immigration violation. This was a man who first raised suspicions with the US authorities because he enrolled in a flight school to learn how to fly passenger jets, even though he did not have so much as a basic pilot's licence.

Perhaps most pertinently, this was a man who had been the subject of numerous official warnings from French intelligence ­ warnings that apparently went unheeded by the Americans and by the British authorities.

It is also clear that there was something very fishy about his plans to learn to fly in the US. It was an odd career choice for someone with a Masters degree in international business from South Bank University. It was an even odder choice for someone who showed no propensity for flying, failed in his first attempt to obtain a licence, and who seemed out of step with his fellow students.

It remains to be seen exactly what evidence the US authorities have gathered on the 33-year-old Mr Moussaoui, but the circumstantial case against him is made in yesterday's 31-page indictmentmn which details many of the known facts about al-Qa'ida and Osama bin Laden's declared jihad against the United States.

It states that from 1992 Mr bin Laden and others attempted to obtain components of nuclear weapons and issued fatwas that US forces in Saudi Arabia, Yemen and Somalia should be attacked. It names al-Qa'ida's Khalden training camp - among others - in Afghanistan and identifies Mr Moussaoui as being there "in or about" April 1998.

The US theory is that he was sent by al-Qa'ida for training as a pilot, exactly like the 19 men who ended up participating in the suicide hijacking plot. After he failed to obtain his licence he was put on the backburner as a potential participant, then reactivated over the summer when the putative 20th hijacker, Ramsi Bin Al-Shibh, failed to obtain a visa to enter the US.

According to French and US investigators, Mr Moussaoui received about $15,000 (£10,700) in two instalments from the al-Qa'ida cell in Germany, where the attacks on the Pentagon and the World Trade Centre were formulated, and immediately transferred from Norman, Oklahoma ­ site of the first flight school he attended ­ to Eagan, Minnesota, just outside Minneapolis, where he sought training on flight simulators to teach him how to fly a jet at cruising altitude. He expressed no interest in learning how to take off or land.

His behaviour was suspicious enough for the PanAm Flight Academy to call the police, which is why he ended up in jail. And he had raised suspicions before. When he applied to the school in Oklahoma, he refused at first to give his real name, preferring to go by the pseudonym Zuluman Tango Tango. His e-mail user name, registered in Malaysia, was pilotz123.

Moussaoui liked to use a lot of pseudonyms. According to the indictment, his aliases included Shaqil and Abu Khalid al Sahrawi. But one monicker seems particularly intriguing, the name he used when introducing himself to his flight-school classmates in Oklahoma: Shakur. The same name has recently surfaced in a Spanish investigation of links between Madrid-based members of al-Qa'ida and their interlocutors elsewhere in Europe.

According to telephone transcripts released by the Spanish authorities, the suspected head of the Madrid al-Qa'ida cell, Imad Eddin Barakat Yarkas, had repeated conversations in late August and early September with a man identified only as "Shakur". It seems unlikely, although not impossible, that this "Shakur" was Mr Moussaoui, since he was in custody in Minnesota at the time after his arrest on a visa violation. Nevertheless, the coincidence of the name could well point to links between Mr Moussaoui, his fellow Islamic radicals in London, where the second "Shakur" appears to have been, and al-Qa'ida's European network.

While training Mr Moussaoui chalked up 57 hours of flight but still did not make the grade, even though students can usually fly solo after 16 hours. The instructor Azim Suman said Mr Moussaoui was "stubborn ... he would not listen and gripped the controls with all his might". "I hope I never have to fly with him," he said.

Mr Moussaoui socialised only with fellow Muslims and attended a local mosque. Occasionally he was overheard saying it was wrong to look at cheerleaders or basketball players because they were "naked". He thought that excessively long trousers were a violation of Islam.

Mr Moussaoui did not obtain his licence and abandoned his course in May, although he continued to live in Norman.

He also made inquiries about opening a crop-dusting business in Oklahoma ­ an interest that raised the possibility that he was involved in a plan to disperse chemical or biological agents from the air.

When the decision was made to move to Minnesota, Mr Moussaoui travelled with a friend, Hussein Al-Attas, who was arrested with him on 17 August and then rearrested after 11 September and moved with Mr Moussaoui to the Metropolitan Correctional Centre in New York. The indictment says that at the time of Mr Moussaoui's arrest he had in his possession items including, knives, binoculars, flight manuals for a Boeing 747, a flight simulator computer program and computer information about applying pesticides from a plane.

Mr Moussaoui has refused to co-operate with the inquiry, and it seems much of the work since his arrest as a material witness has been in piecing together possible links between him and al-Qa'ida. His relationship with Abu Qatada in London is clearly one key area. So too are his trips to Afghanistan. There are also reports of extensive telephone contact with Bin Al-Shibh and other suspects in Hamburg. Of these elements, the first big case to emerge from 11 September will surely be made.