The five key bomb suspects
THE Moroccan is the first person to have been named as a possible suspect. The 44-year-old British citizen was convicted in absentia for his part in a Casablanca suicide bombing in May 2003 which killed 33 people, and is believed to be at large in London
Gerbouzi is said to have been living with his family in Britain for 16 years. It is understood he was granted indefinite leave to remain in the country, despite warnings from Morocco that he posed a threat.
A former pupil of cleric Abu Qatada - said to be Osama bin Laden's European "ambassador" - Gerbouzi is also alleged by the Spanish authorities to have links with last year's Madrid bombings.
He denies any involvement in terrorism.
ZEESHAN HYDER SIDDIQUI
A 25-YEAR-OLD British national who allegedly trained to make bombs in an al-Qaeda camp, he was arrested in Pakistan in May.
Siddiqui apparently told the Pakistani authorities that he was from West London and had read economics at a London University.
"Siddiqui could be vital to solve this puzzle," said a Pakistani official.
"He could lead the authorities to any other sleeping cells linked to al-Qaeda in the UK."
He is one of a number of suspects already in custody abroad whom investigators will be keen to speak to.
MUSTAFA SETMARIAN NASAR
THE alleged mastermind of last year's Madrid railway bombings who also goes by the name Abu Musab al-Suri. The Syrian is suspected of being al-Qaeda's operations chief in Europe and has emerged as a suspect in the London attacks, according to unidentified investigators cited in Sunday newspapers.
Nasar, 47, is a known ringleader of terrorist group Abu Hafs al-Masri Brigades, one of three al-Qaeda groups to have claimed responsibility for the bombings.
He is thought to have lived in London between 1995 and 1998 but is now believed to be in Iraq.
Police in Spain have already accused him of establishing sleeper cells in London, Madrid, Rome, Paris and Milan.
MOHAMMED JUNAID BABAR
IN CUSTODY in the US after he admitted assisting in a bombing plot in Britain.
The New York man, originally from Pakistan, is believed to have been associated with a group in London known as al Muhajiroun, which includes Pakistani terrorists.
Al Muhajiroun was under British surveillance and members of the group purchased nearly a tonne of ammonium nitrate, a raw material used to make bombs. British police foiled an apparent bomb plot in March last year when they arrested eight men and seized about 600 kg of ammonium nitrate from a self-storage warehouse in West London.
Babar, 30, last year also admitted smuggling money and military supplies to a senior member of al-Qaeda in Pakistan and setting up a jihad training camp.
ABU MUSAB AL-ZARQAWI
INVESTIGATORS are thought to be looking into whether Iraqi explosives provided by al-Qaeda's top agent in Iraq were used in last week's terror bombings.
A US official said police have linked al-Zarqawi to the attacks because of the vast amount of explosives and munitions in Iraq.
Homeland security secretary Michael Chertoff said officials were "concerned about" a possible al-Zarqawi link.
"I want to withhold judgment. We haven't seen any definitive indication of that," he said.
"It's something we obviously want to look to, we're concerned about."