Intelligence sources tell NBC News that the British have identified a fifth man seen on a surveillance tape with the bombers but are trying to determine his role. Sources also say that the bomb detonators were inside cell phones.
Intelligence sources believe the fifth man is tied to the bomb-making factory in a Leeds neighborhood, which was searched again on Wednesday. Police hauled away the car — found to contain explosives — that they believe three of the bombers drove to Luton.
"This cell looks like a classic operation where they come from out of town, they meet at a pre-designated spot, they're given the wherewithal and the bombs, and they go off and do their deed," says terrorism analyst Steve Emerson.
Law enforcement officials tell NBC News that police have tentatively identified the fourth suspected bomber as Lindsay Germeine, a Muslim of Jamaican descent living in the area.
The other suspected bombers are all British citizens of Pakistani descent: Mohammed Sidique Khan, 30, a married father of an 8-month-old baby; Hasib Hussein, 19, who friends say became more religious in the last couple of years; and Shehzad Tanweer, 22, a university student who loved soccer.
A neighbor who did not want to be identified recalled a recent conversation with Tanweer.
"He said, 'I went to Afghanistan for a couple of months and stayed there' and he stayed in Pakistan for four months at Lahore," said the neighbor.
Neighbors say two of the men recently returned from Pakistan. Two also prayed at the local Tablighi Jamaat mosque, a fundamentalist Muslim group sometimes known for extremism.
"There may be people involved in recruitment, indoctrination and handling of the suspects, the construction of the device and, crucially, of course, someone to order the operation to be carried out," says Charles Shoebridge, an NBC News terrorism analyst.
Wednesday night, Western intelligence sources say the operational chief of al-Qaida, Abu Faraj al-Libbi, now in U.S. custody, has been questioned about the attacks and so far has disclosed nothing.