Detectives are piecing together the lives of Britain's first suicide bombers - four home-grown young men who are believed to have brought carnage to London.
And they are also hunting the mastermind behind the attacks that killed 52 people, amid fears there may be more volunteers ready to die for their cause.
Three of the four bombers are believed to be Shehzad Tanweer, 22, of Leeds, Mohammed Sadique Khan, 30, of Dewsbury, and Hasib Hussain, 19, of Leeds.
A fourth man from Yorkshire, who police have now identified, is believed to have been on the train which was devastated near Russell Square Tube station.

Bashir Ahmed, 65, the uncle of Shehzad Tanweer, has spoken of his family's devastation.
"The family is shattered. This is a terrible thing."
Mr Ahmed said it was hard for the family to accept their son had caused such loss of life, adding: "It wasn't him. It must have been forces behind him."
Sky News' Crime Correspondent Martin Brunt said police "believe it is highly unlikely that these men were working on their own".
A car containing explosives has been removed
He added: "They have to assume that there were others working with these four."

Security services fear there could still be a second suicide bomb team waiting to strike and that any al Qaeda mastermind may have already fled the country.
Police are now focusing efforts on Leeds, where homes have been raided, and Luton, where two cars thought to have been used by the suspects were found.
Detectives were led to Yorkshire after documents belonging to the four were found at the blast sites.
One of the men had been reported missing by his mother after the attacks, apparently worried he may have been caught in the tragedy.
Friends of another man said he had travelled to Afghanistan and Pakistan within the last six months, prompting fears he may have attended an al Qaeda training camp.
A relative of one of the men was arrested in West Yorkshire and is being questioned by the anti-terrorist branch

...and how many more are training in Britain - YOUR country - right now?
We don't need to let them in any more - Britain now has a new 'industry' - we are letting lunatic Fundamentalist Islamic terrorists of Al Qa'eda Europe train and equip themselves in our country. How long will this madness go on? Non-European immigration should be halted NOW and a full policy of repatriation started.