One of the July 7 suicide bombers made three desperate phone calls to his fellow terrorists just before detonating his explosives, it has been reported.
Hasib Hussain, 18, is thought to have been planning to board a Northern Line train towards Euston on the morning of the attacks, but was frustrated when the service was suspended.
Security sources told the Evening Standard that after the time passed when the explosions were supposed to take place, Hussain used a mobile phone to try to call his accomplices with "increasing panic".
However, the other three had already detonated their devices in the Underground and did not answer.
Seconds later Hussain blew up the Number 30 bus in Tavistock Square, killing himself and 13 passengers.
The Evening Standard said investigators believe the calls prove that the attackers had not originally intended to target the bus.
They are also thought to indicate that there was no al-Qa'eda "mastermind" or wider support network, otherwise the confused terrorist would have phoned them for help.
Under this theory, according to the Standard, the July 21 bombing attempts seem likely to have been a copycat strike carried out by people who were under a false impression that the first bombers had planned to hit three Tube trains and a bus.