Reid attended this mosque in south London
Richard Reid is in custody in the United States after allegedly trying to set off a bomb in his shoe during a Paris-Miami flight at the weekend.
Abdul Haqq Baker, the chairman of the Brixton mosque in south London, said he warned police about extremist elements operating in the area five years ago.
Mr Reid, 28, also shares a connection with Zacarias Moussaoui - the only person so far charged in connection with the 11 September terror attacks in the US.
Both men had been worshippers at the Brixton mosque in south London.
Assault
US officials, quoted on CNN, said several men detained in Afghanistan have said they recognised Mr Reid from terrorist training camps in the country.
But so far there has been no confirmation that he was part of the al-Qaeda network.
The FBI said it would be charging Mr Reid with assault and intimidation of the crew of American Airlines Flight 63 from Paris to Miami. He is due in court on Friday.
The Boston Globe newspaper said the FBI believed Mr Reid was part of a "wider network" of Islamic extremists.
'Extreme elements'
Mr Baker, chairman of Brixton mosque in south London, has told the BBC that Mr Reid, who is believed to be of Anglo-Jamaican heritage, came to the mosque to learn about Islam but soon fell in with what he called "more extreme elements".
Mr Baker said Mr Reid had converted to Islam while serving time in a British prison for minor offences.
But he said he later became convinced his teachers were too "passive" in the face of perceived Western injustice.
He said he came into contact with "more extreme elements" in London's Muslim community, started wearing military gear and talking about fighting a jihad or holy war.
Mr Baker said: "He said we had to revolt against the rulers of the Muslim countries, because they were not actually Muslims."
He said Mr Reid said Muslims who lived in Western society should make plans to revolt against and undermine it.
Mr Baker said there were perhaps as many as 1,000 extremist Muslims in the UK, of whom at least 100 were ready to become suicide bombers.
He said: "Those propagating the extreme views are relatively few in number but in the last four or five years we have witnessed that number grow quite frighteningly."
Mr Baker said he warned police of his concerns about extremist elements, but no action was taken.
A Scotland Yard spokesman said they could not comment on specific cases.
When Mr Reid was searched he was apparently found to have "two functional explosive devices" in his shoes, which contained C-4, a type of plastic explosive.
The suspect had reportedly been prevented from boarding a similar flight in Paris the previous day because he was acting suspiciously.