Piece by piece, the jigsaw of terror revealed

Investigators now say they have pieced together more or less the whole jigsaw of the plan to attack America but are missing one vital ingredient: a firm, compelling link with Osama bin Laden.

They now know that the hijackings were conceived as far back as 18 months ago and were developed in a student apartment in Hamburg, shared by the main instigators, Mohamed Atta, Marwan Al-Shehhi and Ziad Jarrah. By examining the flow of money through the bank account of Atta, suspected of being the ringleader, they have established the operation cost $500,000 and was funded from bank accounts in the Middle East.

The degree of planning and the network's global reach have left agents in the US and in Britain stunned. Each of the four planes was supposed to carry five hijackers. Each gang was divided into trained pilots who commandeered the controls, and armed "minders" who kept the passengers and crew at bay. The leaders on each aircraft had been in the US for some time and were joined by the lesser lights more recently.

The plan worked brilliantly, with one exception: the aircraft which crashed near Pittsburgh. Its complement was one man down because a 20th hijacker, Zacarias Moussaoui, had been arrested in Minnesota. Moussaoui, who has refused to co-operate with the authorities, was having lessons on a flight simulator and aroused suspicions because he showed no interest in learning how to take off or land a plane.

A key role in the build-up, the FBI claims, was played by Lotfi Raissi, the Algerian pilot who lived in Britain and who is now resisting extradition to the US to face possible charges of conspiracy to murder. Raissi who lives in Colnbrook, Berkshire, made frequent visits to the US and was caught on video flying from Las Vegas to Phoenix in June this year with Hani Hanjour, believed to have been the pilot of the plane that crashed into the Pentagon.

Raissi had previously lived in the US and, the FBI alleges, used the social security number of a dead woman. FBI investigators admit to being astonished by the ease with which the terrorists and their possible accomplices acquired false identities, immigration papers and drivers' licences.

However, in the past few days agents have started to rule out the possibility that the hijackers were guided by a US-based mastermind. Instead, they believe the group plotted the atrocities themselves, taking instructions from no one else; or if they did, the FBI thinks, then that person was in Europe, possibly Germany. The FBI is sending more agents to Germany where they will try to establish whom Atta met when he returned to Germany from the US on at least two occasions. They also believe Atta's visit to Spain early this summer was a critical part of the planning process.

Four of the hijackers received training in Bin Laden camps in Afghanistan. This, at the moment, is the strongest link produced by the mammoth inquiry to the fugitive extremist leader. While investigators have built up a detailed picture of the hijackers, they confess to frustration that they are still lacking proof of direct involvement of Bin Laden or his deputy, Ayman Al-Zawahiri.

Colin Powell, the US Secretary of State, went on television last weekend to promise the release of a dossier proving Bin Laden's connection to the hijackers. Since then, privately, officials have been backtracking: there will of course be gaps in the document when it arrives because they cannot print any classified information; the report is likely to concentrate on circumstantial, "soft" evidence as opposed to conclusive, hard fact.

Publicly, the FBI believes "one or more" of the hijackers was linked to Bin Laden. Privately, officials say they believe two of the 19 were members of Bin Laden's Al-Qa'edah organisation – but they cannot prove it.

They cite the tale of Herbert Villalobos as indicative of the difficulties they face. On 2 August this year, Villalobos and his friends were standing in the parking lot near the office of the Virginia Department of Motor Vehicles in Arlington when three men pulled up in a van and asked him if he could help in getting them Virginia state ID cards. Villalobos got in his car with his friends and, with the three following behind, drove to a nearby attorney's office.

There, Villalobos signed papers testifying that one of the three, Abdulaziz Alomari lived in Virginia. One of Villalobos's friends, whose identity the FBI is keeping secret because he is a witness, also signed papers for another of the three, Ahmed Saleh Alghamdi. Alomari and Alghamdi were to die on the same day, 11 September. Alomari was aboard American Airlines Flight 11 as it ripped apart the north tower of the World Trade Centre. Alghamdi was aboard United Airlines Flight 175 that followed minutes later, smashing into the south tower.

The seven-page affidavit of FBI special agent Brian Weidner does not record his own emotions in tracking down Villalobos and his friend and interrogating them. If it did, the testimony would surely have recorded excitement giving way to disappointment as it became obvious Villalobos and his pal were just another blank for Weidner and his colleagues.

At first, when they discovered an office linking the two aircraft and the hijackers, the agents thought they were on to something. In order to purchase the airline tickets, Alomari and Alghamdi had to present some form of ID. When the IDs were checked, the FBI suspected they were looking at a terrorist cell, possibly still operating, in Virginia. When they looked at the name on the papers of Alomari they saw the name Oscar Diaz. Then, when they discovered Diaz was not a real name, they really thought they had cracked it. More police work led them to Villalobos, alias Oscar Diaz, and the depressing realisation that he was a chancer who just happened to be in the car park when the three men pulled up. There is no bombers' network centred on the Virginia Department of Motor Vehicles. Villalobos has been charged with helping someone procure a false licence. This story is just one of many doing the rounds among the inquiry teams.

When the planes crashed, the FBI rushed to do what they do best: seizing flight bookings, credit card slips, car rental and hotel records. Establishing who the hijackers were was not difficult; discovering how they came to buy plane tickets was easy, too. After that, well. You try piecing together the lives of 19 people, officers say, many of them with false names, spread out across America, in an America which until 11 September did not care about them, which even let some of the hijackers into the country despite their names appearing on immigration "watch" lists, which even helped them get bum IDs in a parking lot. And see how you do.

The FBI did well. Slowly but surely, partial biographies of the hijackers emerged and pictures, too. What this progress does not seem to do, according to noises coming out of the inquiry, is to take the bureau any further. There are leads but they appear to be dead ends: low-lifers in car parks; solid, respectable owners of rented houses; clerks in car rental offices; managers of flying schools.

The hapless Villalobos does not work for Bin Laden (it is doubtful if, before 11 September, Villalobos, like many Americans, had ever even heard of him) and neither, worry investigators, do most of the others so far caught in the FBI's dragnet. This is why the agents who set out with such urgent determination on 11 September are beginning to feel crushed – weighed down by the global scale of the inquiry and the sheer difficulty of making a case against Bin Laden stick.

From the moment it became clear that this was deliberate mass murder rather than some ghastly accident, the FBI has been swamped. The phones have never stopped, the e-mails continue to pour in. At the last count, the FBI had 62,232 separate leads to explore.

How many of them yield solid evidence remains to be seen. These were hijackers who knew they were going to kill thousands, could predict America's response and, as a result, it would seem, left no trace beyond the meaningless.

Secrecy was not a new phenomenon for them. They had been leading double lives long before 11 September, duping their families into believing they were smart, ambitious, good boys – with a bit of Islamic fervour thrown in. They were well versed in the art of removing the evidence, of making sure they were not found out.

Several of them were on immigration "watch" lists and must have suspected so (they were not to know the US intelligence system was so poor that they never came under surveillance), so they were careful, living quiet, clean-cut lives.

On the day of the attacks the FBI's 56 field offices were told in a conference call from their deputy director in Washington, Tom Pickard, that it would not be an easy case. So why, by the end of the first day, were US intelligence officials saying they were "90 per cent sure" that Bin Laden and his Al-Qa'edah group were responsible? Today, US officials maintain they are more than 90 per cent sure – but they are still not 100 per cent. The firmest evidence they are prepared to acknowledge against Bin Laden, in addition to the four, unspecified hijackers having spent time at his camps, is as follows:

* Within hours of the attacks, the US National Security Agency intercepted phone calls from known Bin Laden supporters boasting, "we've hit the targets". More details of these calls, such as who made them, when and to whom, are tightly guarded. The White House press secretary, Ari Fleischer, has made it plain that some evidence will be withheld: "[The terrorists] would like nothing better than to be able to hide where they are hiding and have the US reveal what we know and how we know it. We're just not going to do that." Presumably, the people who said "we've hit the targets" know they said it and now must be aware their phones are being tapped. How that fits in with the Fleischer doctrine is hard to fathom. But intelligence officials claim the calls were made, so we should believe them.

* Atta is thought to have belonged to Islamic Jihad, the Egyptian extremist group founded by Zawahiri, Bin Laden's deputy. Islamic Jihad is part of the loose Al-Qa'edah grouping. Zawahiri is already under indictment in the US for the embassy bombings in Kenya and Tanzania.

* Khalid Almihdhar, suspected of being a hijacker on American Airlines Flight 77 which hit the Pentagon, was filmed by the CIA in Kuala Lumpur in January last year meeting a suspect in the bombing of the USS Cole, an attack attributed to Bin Laden.

* Investigators believe Nabil Al-Marabh knew at least one of the hijackers (they are not saying which one). Al-Marabh was arrested after the attacks in suburban Chicago where he had been working in a liquor store. The FBI were already looking for him before 11 September because of his close ties to Raed Hijazi, a self-confessed Bin Laden supporter in jail in Jordan for trying to blow up a hotel filled with American and Israeli tourists. Al-Marabh wired money to Hijazi in Jordan. Both men had previously been together in Boston. Despite the FBI's excitement in finding Al-Marabh, there are doubts about his worth. He had gone to Chicago after breaking probation, following a stabbing conviction in Boston (he attacked a roommate after an argument) – hardly the behaviour of a terrorist anxious to stay out of trouble. Workmates say he was a lazy, short-tempered womaniser. The authorities counter that this was deep cover, a double bluff by a dedicated Bin Laden operative. They point to the fact that he went out of his way to acquire a heavy goods licence specifically allowing him to transport hazardous materials as evidence of planning for a new atrocity.

More may follow. Investigators are certain they have foiled other planned hijackings and attacks, some of the perpetrators of which are among the 350 or so under arrest. (According to John Ashcroft, the Attorney General, a further 400 are on the FBI wanted list.) In a former home of Al-Marabh in Detroit, the FBI arrested three Arab men and uncovered false immigration papers. Two of the men worked for Sky Chefs, a catering firm at Detroit airport. Among the documents seized were airport diagrams and notes about a US base in Turkey.

Agents found that two of the hijackers' plane tickets had been bought with a credit card belonging to the same man, Al-Badr Al-Hazmi, a Saudi national (almost half of the 19 came from Saudi Arabia) working as a radiologist in San Antonio.

Dr Al-Hazmi was duly arrested. When it was discovered he had bought three tickets for himself to fly on 22 September, agents thought they had uncovered a second wave of attacks. He claims the two extra tickets were for his wife and child. It is possible the hijackers used the card without him knowing (the terrorists were adept at stealing other people's identities). He is now in New York, due to appear before a Grand Jury.

The FBI is also poring over the past of Khalid Al-Draibi, a Saudi arrested on the same day as the attacks, driving away from Dulles airport. In his car, police found aviation manuals. He had used 10 different names since entering the US in 1997 and obtained driver's licences in five states. Like the hijackers, he had taken flying lessons. He insists he is the victim of unfortunate coincidence.

There is also Moussaoui. He was arrested on 17 August. The flying school instructor took his concerns to the FBI which arrested him on immigration charges. Checks revealed he was wanted in France in connection with terrorist attacks. He had attended Bin Laden camps in Afghanistan and recruited Muslims to fight in Chechnya and Kosovo. Until February of last year, Moussaoui is believed to have lived in Brixton, south London.

His mother, who lives in Narbonne in southern France, said he had been "brainwashed" by Islamic extremists during his time in London. British police want to interview his former girlfriend, but have not named her.

Two other major suspects are Mohammed Jaweed Azmath and Ayub Ali Khan. They were held on an Amtrak train in Fort Worth, Texas, the day after the attacks. They were carrying hair dye, a large quantity of cash, and knives similar to the ones used in the hijackings. They were booked on a flight from Newark to St Louis which was grounded in the aftermath of the attacks. Both of them had been to flying school.

All the evidence gathered so far suggests that it was in Germany that the hijackers plotted their attacks. Atta, Al-Shehhi and Jarrah lived in Hamburg for several years before they moved to the US. There they met Syrian businessman and financier, Mamoun Darkazanli. He is one of 27 individuals and organisations whose assets were frozen by President Bush last Monday for suspected involvement with terrorism.

Following raids on properties in Hamburg, the authorities there are also searching for Rimaz Binalshibh from Yemen and Said Bahaji, a German.

Though alarm was raised last week when it was disclosed that 11 of the 19 hijackers had passed through Britain on the way to the US, intelligence sources believe the most senior members of the Al-Qa'edah network based here were already in prison awaiting extradition before the attacks of 11 September.

The fact that the hijackers visited Britain may not be significant. "This may well be a tribute to the success of Heathrow and Gatwick airports as transit hubs rather than evidence of the hijackers being based in Britain. At the moment there is no hard evidence that they spent any great time here," said a Whitehall source. "Press reporting has been somewhat hysterical over this." And, despite a number of people linked to Bin Laden having gone to ground in Britain, it is not thought, despite claims to the contrary, that there is a high chance of them undertaking terrorist actions in the near future. "The networks associated with Bin Laden have taken quite a hit over the last 12 months," said a British intelligence source.

"We are not complacent and we are keeping a close eye on these Middle Eastern connections, but we don't feel there is a imminent problem." British intelligence is also playing down the likelihood of a biological or chemical warfare attack.

During the week, the Foreign Office minister Peter Hain said he thought Bin Laden was planning further attacks, in Britain. "We are in a very dangerous situation. I understand that he is preparing already for high-impact terrorist attacks in the coming weeks, if he is able to." But on Friday, Tony Blair's official spokesman denied this by insisting there is no evidence of a specific threat against the UK. The spokesman said: "Speculation about UK connections to the attack on the United States is exaggerated. At this stage in the investigation, both the US and the UK authorities have no reason to believe there were significant British connections to these attacks."

Terrorism experts believe that MI5 and MI6 are doing a good job of containing the threat from the Middle East. "Britain has been extraordinarily effective in detecting and degrading the individuals involved in these terrorist networks here," says Magnus Ranstorp of the Centre for the Study of Terrorism and Political Violence at St Andrews University. "They have been more effective than any of their European counterparts."

In addition to Raissi, five people have been arrested in Britain since the World Trade Centre attacks. Three men were arrested in Leicester and at least one, Kamel Daoudi, was questioned by Special Branch about a plot to attack the US embassy in Paris. He is suspected of being involved with the fundamentalist group Takfir wal Hijra. Six men and a woman were taken into custody in France in connection with the planned attack.

In Britain MI5 devotes about a fifth of its resources to monitoring Islamist extremists. "The British problem is small compared to Germany, where the Interior Ministry estimates that there are around 4,400 Islamic extremists living, some violent, some not," says Dr Ranstorp. He says that terrorist use different European countries as their bases depending on which immigration and financial documents are available to the group.

"The instruction to commit the act and an approximate timing may be sent down from on high, but the actual organisation and details are arranged at a local level," he adds.

Some 40 suspected members of these networks have been arrested since 11 September. Material seized at addresses across Europe has revealed further planned outrages. Six Algerians arrested in Spain appear to have been planning suicide attacks on US interests in Europe. Videos seized during raids showed footage of Afghan terrorist training camps.

But Britain appears to have flushed out many of the major players in the Bin Laden networks following the FBI investigation into the suicide bombings of the US embassies in East Africa in 1998. Special Branch raided a house in Manchester in 1998 used by Ibn Al-Shaykh al-Libi. He is another of the 27 individuals and organisations named by President Bush.

Dr Ranstorp says that police believe that al-Libi, a Libyan, is suspected of carrying out the reconnaissance of the US embassy in Tanzania prior to its destruction in 1998, an operation mounted by Bin Laden's associates. "He reported back to the Al-Qa'edah military committee who sanctioned the attack," says Dr Ranstorp. In his terraced house in Manchester they found a 180-page book in Arabic, Military Studies in the Holy War against Tyrants, which was presented in the later trial of the bombing suspects as a "how to" guide for terrorist acts.

Three men have been in British prisons since 1998 fighting extradition to the US. There they face trial for the East African bombings. One of the men is Khalid al-Fawwaz who is thought to be a senior member of Al-Qa'edah and a critical member of the Bin Laden organisation.

From his arrival in London in 1994, al-Fawwaz ran Bin Laden's propaganda operation in Britain. Later he is alleged to have set up the base in Nairobi for Al-Qa'edah that was used for the 1998 bombings. He returned to Britain after being arrested in Kenya over a minor matter.

Another key figure awaiting extradition is Abu Dohar who, authorities believe, is a key figure in the North African jihad network. He was arrested after Ahmed Ressam, an Algerian who lived in Montreal, was detained on the US-Canadian border with explosives. Ressam was planning to bomb Los Angeles International Airport on Millennium Eve. During his interview Ressam told police he was a follower of Abu Dohar, who was an associate of Bin Laden. Seized from Dohar's flat were three passports, 200 propaganda video cassettes about the jihad in Chechnya, 100 black berets, a telescopic rifle sight and blank Italian, French and Spanish passports.

In February, police in London detained 11 men, most of them Algerians, on terrorism, fraud and forgery charges after police in Milan uncovered a plot to attack a US target in Strasbourg.

"We believe that among those locked up waiting to be sent to the US or Europe are Bin Laden's closest associates based in Britain," said an intelligence source.

Dr Ranstorp says that while British intelligence has problems penetrating the tight-knit world of Middle East terrorism, they do get good information from those who are arrested.

"Ahmed Ressam, for instance, gave a great deal of information about how these networks operate," he says.

In the US meanwhile, the FBI is flinging over stones – and finding horrific evidence of suggested further outrages being prepared.

Al-Marabh was not the only Islamist extremist to have acquired a licence to drive toxic and hazardous loads: the FBI has 20 on its list; 10 have been caught; 10 are still at large. They know that Atta inquired about crop sprayers. They wonder what else he thought about. It is as if one nightmare has sparked another.