The potential ringleader of the four suicide bombers in last week's attack on London's transit system is alive and still at large.
Authorities tell ABC News they know the identity of the fifth suspect in the London bombings. Video surveillance tapes from the Luton train station, located outside of London, show him seeing the four bombers off the morning of the attack. Although his name has not been released to the public, police sources describe him as having dark skin.
"It is quite obvious that this cell consisted of several other individuals," explained M.J. Gohel, a terrorism analyst at the Asia-Pacific Foundation. "The important thing to establish is how many other associates are there. How big is this cell? And is it likely to perpetrate another atrocity?"
Today police focused their investigation on the middle-class, largely Pakistani neighborhoods in Leeds, where the young bombers lived. British newspapers have dubbed them the suicide bombers of suburbia.
Shehzad Tanweer, 22, whose bomb exploded at the Aldgate station, was best known by his neighbors for his love of playing cricket. Bashir Ahmad, Tanweer's uncle, recalled that his nephew had recently returned from religious training in Pakistan and credited that training with a change in his nephew.
"It wasn't him," Ahmad claimed. "It must have been forces behind him."
Hasib Hussain, 19, who carried the bomb onto the double-decker bus, lived in the Holbeck suburb of Leeds with his parents, who had reported him missing last week. They were apparently unaware that his trip to London with friends was a suicide bombing mission.
"He were a good pillar to the community," recalled Paula Baker, a neighbor of Hussain. "I can't say nothing else because he was."
Mohammed Sadique Khan, 30, who carried the Edgware Road subway bomb, left behind a wife and an infant daughter. Leaders from a local mosque said he and some of the others practiced martial arts in the basement of the mosque.
"A very pleasant bloke. Not an extremist or someone that talk about religion," said Imran Daman, a neighbor of Khan.
However, British authorities explained that these identities were simply good covers for members of a classic sleeper cell. Police today said a deserted house in Leeds, where weapons and more explosives had been discovered, was used by the men as a secret bomb factory. They also expressed fear more bombs remain undiscovered. Today at the Luton train station, located outside of London, police detonated explosives in the rental car left behind by the bombers on their way to London.
Finally, investigators tell ABC News that they know much more about the bombs used. The timers were cell phones, like those used last year in the Madrid bombings. Fragments from the cell phones have been recovered from the bodies of two of the suicide bombers.
ABC News Consultant Alexis Debat, Rhonda Schwartz, Jill Rackmill, David Scott and Madeleine Sauer contributed to this report.