Britain has requested the extradition of Hamdi Issac, 27, who is suspected of trying to bomb the Shepherd's Bush subway station in west London and was detained in the Italian capital on Friday. Issac's lawyer says her client is likely to fight the extradition attempt.
Italian police gave a briefing on Monday detailing how they tracked Issac to his brother's apartment in Rome.
They also said the Ethiopian-born suspect used the fake name Osman Hussain and said he was a Somali to claim refugee status in Britain several years ago.
They added that they expected to extradite him to Britain in a short time.
Issac was arrested in Rome at the apartment of his brother Remzi Issac, who also was detained.
On Sunday, Italian police detained a second brother, Fati Issac, for questioning.
In Britain, police were questioning the three other men suspected of trying to detonate bombs in London subway trains and a double-decker bus on 21 July.
In total, officers are holding 18 suspects in connection with the attacks, including six men and a woman arrested on Sunday in Brighton, on England's southern coast.
Italian police say Issac used a
Police say the four bombers who carried out the 7 July attacks, which killed 52 victims, are all dead. They believe they have arrested all the failed 21 July bombers, whose explosives detonated only partly and took no lives.
They are searching for those who may have recruited and directed the attackers and built the explosives, anxious to catch them before they - or other would-be bombers they command - strike again.
Investigators are also searching for links between the two terror cells, one made up mostly of Pakistani British citizens and the other mainly of East African immigrants to London.
The groups struck exactly two weeks apart.
"It's extremely likely there will be other people involved in harboring (suspects), financing and making the devices"
London Metropolitan Police spokeswoman
A spokeswoman for London's Metropolitan Police said investigators believed there were more people at large who played some role in the attacks.
"It's extremely likely there will be other people involved in harboring (suspects), financing and making the devices," she said, speaking on condition of anonymity, because the department does not allow her to give her name.
No kill intention
Hamdi Issac's lawyer Antonietta Sonnessa says her client acknowledges his involvement in the failed 21 July attack, but claims the planted bombs were intended not to kill anyone but only to draw attention. Italian news reports had said the bombers were angry about the Iraq war.
Issac also said his cell was not linked to al-Qaida or the 7 July cell, Italian media reported.
Britain was facing questions about how Issac slipped out of the country five days after the attempted attacks, despite a massive police manhunt. Italy's Interior Minister Giuseppe Pisanu says Issac left London's Waterloo station by train for the Continent on 26 July.