The extensive foreign travel of the aircraft "shoe bomber", Richard Reid, in the months before his arrest could provide the link to a well-funded and organised terrorist cell.
His travels included visits to Israel, Egypt, Pakistan, Turkey, France, Belgium and the Netherlands.
Investigators believe that the 28-year-old's travels started in June with a three-week visit to the Middle East, beginning with a flight to Cairo and then moving on to Istanbul before going to Israel.
He is believed to have spent a week in Israel before leaving for Egypt, where he could have met Islamic militants, via the Gaza Strip. Israeli security sources said Mr Reid's arrival in July is now under investigation. They are concerned that he may have tried to contact Hamas Islamic militants.
The Israeli airline El Al confirmed that Mr Reid had flown on one of its planes to Israel after going through a security check of his clothes and luggage, which was ordered because he appeared suspicious.
His next trip was to Pakistan in August where he could have crossed into Afghanistan to attend training camps run by Osama bin Laden's al-Qa'ida organisation. American security sources have said that some captured al-Qa'ida members claim to remember Mr Reid attending the camps.
Mr Reid is believed to have returned to a safe house in Amsterdam before going to Brussels to renew his British passport on 7 December, and returning to the Netherlands.
The BVD, the Dutch security service, said it was investigating the possibility that the shoes packed with C4 plastic explosives had been obtained in Amsterdam. Two days after returning to Amsterdam, he caught the Thalys high-speed train to the Gare du Nord station in Paris.
Mr Reid is due to appear in court today in Boston, where he has been charged with assaulting members of the crew on an American Airlines flight 63, bound from Paris to Miami, last Saturday. He allegedly tried to blow up the aircraft with the explosives in his shoes.
The cost of such travels appears to be far beyond the means of a petty criminal from south London and has increased fears that he could be funded by an organisation.
FBI investigators say he has not co-operated fully in giving them details of his travels and that he appears disappointed in failing to complete his alleged mission to kill the aircraft's 185 passengers and 12 crew.Reuse content