The man suspected of trying to blow up a passenger airplane with explosives in his shoes attended a mosque in Brixton, South London.
Richard Reid - who was carrying a UK passport on the flight from Paris to Miami - attended the mosque after converting to Islam while in prison.
Explosive device was complicated
American security think he may have been part of a group, because the explosive device he was trying to use would have been difficult to build without help.
The Times newspaper even thinks he might have been linked to Osama Bin Laden's al-Qaeda group.
Court appearance on Friday
That's because another man charged in America in connection with September's terrorist attacks was also known to have used the same mosque.
Reid will appear in a US court on Friday. A judge will try to decide if there is enough evidence to keep him in jail while he awaits trial, for assault and intimidation of the crew on the plane.