Police are hunting a man with a pock-marked face who bought the car used in the Ealing bomb attack.
The car had been purchased at Green Lane in Ilford, east London, Deputy Assistant Commissioner David Fry said.
It has also emerged that officers were called to examine the car, a grey Saab 9000, by members of the public on Monday.
The vehicle appeared to have been abandoned, but police took no action because it had not been reported stolen or was suspected of being involved in terrorism, he said.
Police also described how they were given just 27 minutes to locate and deal with the bomb which went off injuring seven people.
Assistant Commissioner David Veness described the attack as a "callous, potentially murderous crime committed with total disregard for the safety of potential victims".
"Twenty seven minutes was given by the terrorists between the call which was first made to a third party and the explosion which took place a few seconds after midnight," he added.
Police also appealed for people who had cameras and video cameras at the scene of the blast to come forward.
Mr Fry, head of the Metropolitan Police's anti-terrorist branch, said: "The scene is still being searched but we have found fragments of blue plastic from a barrel-like container. This is similar to the one used to transport the BBC bomb and also ones in Ireland."
The car dealers where the vehicle was sold have refused to comment. A spokesman for Assured Car Finance Ltd in Ilford, Essex, said: "We are not allowed to say anything."