British investigators have found that the four suicide bombers, who triggered a series of explosions in the city killing 56 people, left a car packed with 16 bombs in London, raising fears of a wider terror network.
The bombs were made by the same person who assisted the second group of would-be bombers.
A number of bombs and components, some packed with nails to cause death and maximum injury, were recovered from a car parked by the bombers at Luton station.
The devices recovered at the station were 'strikingly similar in their configuration and contents' to the unexploded bomb found at Warren Street Tube station on July 21, security sources told The Times newspaper.
The nature and number of bombs point to the existence of a large and well equipped terrorist cell intent on a sustained campaign of attacks.
The quantity or ordnance found in West Yorkshire, Luton and London has heightened police concerns that there are many more than eight men willing to die as 'martyrs', the sources said.
Also read: The London Blasts
The nature of the recovered devices provides concrete evidence of a direct link between the July 7 suicide squad, whose four bombs killed 56 people, and the July 21 group whose four devices failed to detonate.
"This completes the circle. The bombmaker used the same constituents in the devices used in the fatal first attacks and the abortive attempts a fortnight later," a security source said.
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