Security sources in Pakistan are investigating a tip-off that Shehzad Tanweer attended a religious school run by the terrorist group Lashkar-e-Taiba (LeT) during a recent visit to the country. The group's founder has publicly stated that he believes suicide bombing to be the "best form of jihad [holy war]".
The revelation came as Pakistan claimed that it helped thwart a terrorist attack in Britain before the May general election, and that its intervention led to arrests in several countries. However, Pakistani authorities refused to comment on reports that the UK was seeking access to Zeeshan Siddiqu, a 25-year-old British national arrested in May near Peshawar.
Yesterday, British police and security services were concentrating their efforts on tracing the man who masterminded the attacks. They now know the identity of all four bombers but are understood to be looking for a fifth man who appears on the CCTV footage from King's Cross. His picture has been distributed to police in London.
There was also a fresh warning from Charles Clarke, the Home Secretary, that a "large number" of people in Britain had been through radical camps abroad.
"We have to understand that these foot soldiers who have done this are only one element of an organisation that is bringing about this kind of mayhem in our society," he said. "And we have to attack the people who are driving it, organising it, manipulating those people."
Mr Clarke dismissed as "completely and utterly untrue" claims that he had told European Union colleagues that some of the bombers had previously been subject to "partial arrest". But there were suggestions that one of the bombers had been linked to a suspect in a separate anti-terrorist inquiry.
The family of Shehzad Tanweer - whose bomb killed six people on a Circle Line train to Aldgate last Thursday - were yesterday said to have been "left shattered" by the news that the 22-year-old was a suicide bomber. His uncle, Bashir Ahmed, 65, said his nephew went to Lahore in Pakistan for two months earlier this year to study religion, but was "proud to be British".
Pakistani investigators suspect that Tanweer attended one of the many madrassas, or religious schools, run by LeT, which is based in Lahore. The group, which also operates under the name Jamaat ud-Daawa (the party of preaching), has close ties with al-Qaeda and access to munitions and safe houses.
Abu Zubaydah, a senior al-Qaeda lieutenant, was seized in an LeT safe house in Faisalabad in March 2002. The group has also been linked with Hamas and Jemaah Islamiyyah, and Indian security forces believe it is playing a significant role in channelling militants into Iraq.
Most of its membership of several thousand have been through madrassas in Pakistan, and many are familiar with the use of explosives. The group maintains links with other terrorist networks and it is known to solicit donations from the Pakistani community in the UK through its charitable wing.
LeT was founded by Hafiz Saeed, a former professor at Lahore's University of Engineering Technology. In April 2003, he defended the use of suicide bombing, saying: "Suicide missions are in accordance with Islam. In fact, a suicide attack is the best form of jihad.
"Jihad is prescribed in the Quran. Muslims are required to take up arms against the oppressor. The powerful western world is terrorising the Muslims. We are being invaded, humiliated, manipulated, and looted. How else can we respond but through jihad?"
The group runs a number of madrassas, including the Darasitul Islamia madrassa, where six Malaysian students were arrested in 2003 on suspicion of training for Jemaah Islamiyyah activities in Malaysia and Indonesia.
Saeed was delivering a sermon at the madrassa on the day of the arrests.
Meanwhile, the biggest concern for police and the security services is that the bombers could have been acting on the orders of an al-Qaeda mastermind and that there may be another bomb team waiting to strike. The Home Secretary said the security services were checking telephone records to establish whether the bombers were part of a larger organisation.
Alan Capps, editor-in-chief at the US Homeland Security Institute, said he believed that the British authorities would be looking for two more people - one the bomb-maker and the other the leader who would keep the four bombers focused on their task - though they were likely to have left the country a few days before the attack.
"One is a strong personality, probably well-educated, easily able to blend into an international community, confident of himself and well travelled," he said.
"The other is probably well-educated in the technical aspects of creating devices, confident about handling explosives and also probably blends into the community, clearly with a technical background, possibly educated in the West."
He said investigators would want to examine where the explosives came from, which could give a better picture of who they were dealing with. And he warned that the bombers were unlikely to have been the only cell.
"I am sure that there are other cells either in the process of being formed or already up and running and at different stages of preparation," he said. "I think we have to assume that this was part of the al-Qaeda franchise."
Police were yesterday giving out few new details about their investigation, but an MP disclosed that one of the houses being searched by officers in Leeds had been used by the terrorists as an operational base.
Greg Mulholland, MP for Leeds North West, said: "I understand this is where the material may have been stored."
Yesterday, Colin Cramphorn, the West Yorkshire chief constable, said there remained a "potential threat of an explosion" at the search scene. The names of all four bombers have now emerged. They were Tanweer, 22, Mohammed Sadique Khan, 30, and Hasib Hussain, 18.
A fourth man was named in Leeds as Eliaz Fiaz, also known as "Jacksy".
A spokesman for Tony Blair said the Prime Minister was "shocked" to learn the bombers were born and raised in the UK, adding: "He is determined that we should take on this extremism."
By last night, ten of the victims of the London bombings had been formally named but Dr Andrew Reid, the Inner North London coroner, warned it may take weeks to identify some of the others.
'Classes' which teach lessons in hatred of West
THEY claim to provide a respectable religious education, spreading peace and tolerance at the core of Islam's message. But the reality is that they are hotbeds of fanaticism and a training camp for the next wave of terrorists.
Madrassas, such as the one attended for some months by English-born suicide bomber Shehzad Tanweer, were denounced in 2003 by US Secretary of State Colin Powell as breeding grounds for "fundamentalists and terrorists".
A year earlier, Donald Rumsfeld, the US Defence Secretary, said in a leaked memorandum: "Are we capturing, killing or deterring and dissuading more terrorists every day than the madrassas and the radical clerics are recruiting, training and deploying against us?"
Although not a new phenomenon, Saudi wealth and charities contributed to an explosive growth of madrassas during the Afghan jihad against the Soviets. During that war, a new kind of madrassa emerged in the Pakistan-Afghanistan region - not so much concerned about scholarship as making war on infidels.
And madrassas - which in Arabic means "schools" - have recently come to worry western governments and anti-terrorism experts more and more.
Despite Pakistani government pledges to crack down on the camps post 9/11, there has been a recent upsurge in their activities and a welter of reports that they are again training Islamic militants.
Pakistan's Herald magazine reported recently that major militant organisations - including LeT - had begun regrouping in April this year and renovating their training facilities. The magazine reported militants were attending refresher courses at the Mansehra camp in the North West Frontier Province.
Experts say problems at madrassas began in the late 1970s with the onset of the Afghan-Soviet war. The schools provided teaching and training for the Taleban, which in Arabic means "religious seminary students".
The enemy then was the Soviet Union; today it is the US and it allies.
These new madrassas now teach Wahhabism, a rigid expression of Islam that promotes fundamentalist readings of the Koran.
While it is disputed whether the schools provide terrorist training, some have undoubtedly become a viper's nest of hatred and anti-Western thinking.
Recently, the Pakistani president, Pervez Musharraf, a US ally, promised to rein in extremist religious schools, but his efforts have seen mixed results.
Nine of the Bali bombers were madrassa-educated, as was Haroun Fazul, who blew up the US embassy in Nairobi in 1998.