An Egyptian dissident living in Britain was arrested by anti-terrorist police over allegations that he helped two hit men to murder the Taliban's main opposition leader in Afghanistan – an event that many believe heralded the attacks on America.
Yasser al-Siri is also accused of relaying threats against the United States by Osama bin Laden and acting as a mouthpiece for the Saudi militant's support network.
He was questioned yesterday about reports that he helped the two men who murdered the commander of the Northern Alliance to obtain visas. Ahmed Shah Masood is thought to have been killed on the orders of Mr bin Laden and many believe it led directly to the suicide hijackings in America only three days later.
Mr al-Siri, 39, was questioned about a report that the hit men, carrying stolen Belgian passports, entered the country posing as journalists after securing visas with a letter of introduction from the Islamic rights campaigner, who is based in London. Under British anti-terrorism laws it is illegal to help terrorists commit acts of violence at home or abroad.
Mr al-Siri is wanted by the Egyptian government for a failed assassination attempt in Cairo in 1993 on Atef Sedki, a former prime minister, in which a five-year-old girl was killed. He has lived in Britain for eight years, since being granted asylum, and was found guilty of the bomb attack by an Egyptian court and sentenced to death in his absence.
He was arrested at 7am at his home in a former council flat in Maida Vale, west London, as part of an inquiry by the anti-terrorist branch. Detectives also searched his flat and an Islamic bookshop in north-west London.
As well as the assassination plot, he is thought to have been questioned about his organisation, the Islamic Observation Centre, (IOC) which is accused of being a mouthpiece of al-Gama'a al-Islamiyya, an Egyptian group believed to be funded by Mr bin Laden.
But it is Mr al-Siri's possible involvement in the plot to kill the one man thought capable of providing a credible and united opposition to the Taliban regime that is the focus of the inquiry. The investigation raises questions over whether Britain provided the springboard for Mr bin Laden and his supporters' war against the West.
The men who killed Masood used the names of Karim Touzani, 34, and Kacem Bakkali, 28. They went to the Pakistani high commission in Lowndes Square, central London, and applied as journalists for visas to enter the country.
In an unusual move, Pakistan granted multiple entry visas for a year on 16 July this year. Normally only visas allowing single entry are provided, so questions have been raised on the possible role of Pakistan, a past supporter of the Taliban, in the assassination.
The hit men flew to Pakistan, arriving in Islamabad on 25 July, and were granted three-month visas at the Taliban embassy in the city two days later.
Mr Touzani and Mr Bakkali, who were holding Belgian passports stolen two years earlier, are alleged to have presented a letter of introduction to the Taliban visa officials from the "Islamic Observation Centre" of Maida Vale. Describing itself as "a worldwide organisation concerned with human rights issues for Muslims all over the world", it allegedly introduced them as journalists working for the non-existent "Arabic News International" and its television subsidiary.
Mr Touzani, it allegedly said, would be "engaged in journalistic and photographic activity related to various projects serving Islamic affairs in general and the IOC in particular". It asked for help and support for Mr Touzani and ended: "May Allah reward you." It was stamped and allegedly signed on 23 July by Yasser al-Siri.
Armed with their visas, the men crossed from Pakistan into Afghanistan. After working for several days in Taliban-held territory, they went to Masood's base in the Panjshir valley.
There, posing as television journalists, they asked the commander: "When you have reconquered all Afghanistan what will you do with Osama bin Laden?," but before he could answer they blew themselves up, fatally wounding Masood.
The blast killed an aide, Azim Suhail, seriously wounded Masoud Khaili, an ambassador to India, and killed one of the bombers. Masood's guards shot dead the other bomber.
Mr al-Siri has protested his innocence in the matter and told journalists: "I have never met these two men [the hit men]. They have usurped the name of my association."
Mr al-Siri is one of three men living in Britain who the Egyptian government alleged were senior figures in Jihad, also known as the Vanguards of Conquest – a fundamentalist guerrilla organisation.
Egyptian officials claim Mr al-Siri helped to train 36 militants who were arrested in 1995 for planning suicide attacks on ministers, journalists, politicians and policemen. But Mr al-Siri insists the charges are based on testimony given under torture.
His possible links with the al-Qa'ida network have been fuelled by the IOC website, which was the first organisation to report the death of Abu Baseer al-Masri, one of Mr bin Laden's chief lieutenants, during the US bombing of Afghanistan.
The site also relayed a statement purportedly from Muhammad Atef, a senior al-Qa'ida commander, warning that American troops would suffer the fate in Afghanistan that they did in Somalia.
Mr Al-Siri, who claimed benefits for part of his time in Britain, has denied being involved with any terrorist groups and has said he is just a journalist, describing himself as a "messenger" with good contacts in Afghanistan.
The IOC website is a crude affair with two twirling blue bombs at the top of the first page and lines of dripping blood breaking up the various items that provide news stories and allegations of various human rights violations by the Egyptian authorities.
It also contains support for militants including Dr Omar Abdul Rahman, the blind sheikh jailed for the 1993 bombing of the World Trade Centre.
When asked recently about his connections with al-Qa'ida Mr al-Siri reportedly replied: "I am not in any way connected to bin Laden. I don't agree with everything he does."