Travel documents seized in Dublin in September and October by gardaí are understood to have led to a connection with a Middle Eastern businessman who the FBI believe was closely involved in financing the September 11th attacks last year.
The businessman, who disappeared after the attacks, is believed to have been closely involved with Mr Zacarias Moussaoui, the suspected al-Qaeda member now under arrest in the US and awaiting trial on charges of conspiracy prior to the attacks.
Garda investigations into the connections between a number of people still living here and the al-Qaeda group responsible for the September 11th attacks are still under way, according to Garda sources.
A unit set up with the Special Branch in Dublin is monitoring in particular the activities of one man, in his late 30s, who they suspect of supplying travel and identity documents to al-Qaeda prior to the New York and Washington attacks.
It is also understood that gardaí are reappraising their view that al-Qaeda figures here were only marginally involved in the global activities of the organisation.
While financial documents seized here show evidence of generally small transactions within this State, it is suspected that one figure based in Dublin travelled abroad regularly and may have been a key figure in financing al-Qaeda's European operations.
It has emerged that during a search of premises used by this man, gardaí discovered airline travel documents which are connected to the Saudi financier named by the FBI as Mr Mustafa Ahmed al-Hisawi. It is not clear if Mr al-Hisawi ever visited Ireland.
Gardaí also believed that a cell of al-Qaeda members working in Dublin were involved for several years in providing false identification, possibly including passports, visas and other documents to facilitate the movement of al-Qaeda members.
One prominent member of the Dublin group left Ireland in July last year and disappeared after being resident here for almost a decade. He is being sought by the US authorities.
Garda investigations after September 11th into suspected al-Qaeda figures in Dublin led to raids in October on a number of premises in south Dublin. In one office they found the travel papers hidden behind a filing cabinet.
Details of the contents of the documents were passed on to the US authorities. It is understood that some have shown direct links to airline travel which was financed by Mr al-Hisawi.
It does not appear, however, that there has been sufficient evidence to allow the extradition of the man, still resident here, on conspiracy charges.
The suspect who still lives in Dublin has remained under surveillance as part of a Garda operation which has been monitoring the activities of a small group - possibly less than 30 - who are seen as having extreme Islamic views and sympathetic to al-Qaeda and Osama bin Laden.
Gardaí believe the group set up a base here because of the low level of security surveillance of foreign nationals.
Some members of this group have been here for over a decade and are now naturalised citizens. It would be difficult under Irish law to extradite a citizen on conspiracy charges and almost impossible under existing law to extradite someone on suspicion alone.
The man at the centre of the post-September 11th Garda operation when the travel documents were found was arrested recently under suspicion of trying to use a false credit card in Dublin. He was detained briefly and then released.
The close associate of this man who disappeared from his home in Ballinteer, Co Dublin, in July last year was named in an FBI indictment of four men arrested for their role in a conspiracy to plant a large bomb in Los Angeles or Seattle during the millennium year.
One of the figures at the centre of the subsequent trials in the US shared a flat in Vancouver with the suspected al-Qaeda man who left Dublin last year.
During their investigations into the failed millennium attack, the FBI sent investigators to Dublin in October 2000, and gardaí arrested the suspect and a number of other men. They were released, however, when it was determined there were no grounds to hold them.