His family were perplexed when Shehzad Tanweer decided to drop out of his sports science course at Leeds Metropolitan University at the end of last year so he could travel to Pakistan.
He told them that he desperately wanted to join a group of friends from his local mosque on a two-month visit to a religious school near Lahore.
The 22-year-old joked with his parents that he would pick up his education when he came back, adding that it would also give him the chance to visit relatives in his father's hometown, Faisalabad, which was only 100 miles away.
Hasib Hussain's family thought him spending some time with his relatives in Pakistan might curb the teenager's rebellious streak and stop him spending his time hanging around street corners in Holbeck, drinking beer with local youths.
His parents thought their plan had worked when Hussain got back, a much calmer figure and with a new found enthusiasm about pursuing his Muslim faith.
Both families are now left asking themselves whether it was their sons' journeys to their homeland that corrupted them.
Tanweer's uncle, Bashir Ahmed, has no doubts that it was faceless figures in Pakistan who radicalised his sports-mad nephew.
"He was such a calm, loving normal boy. Extremists must have got their hands on him," the 65-year-old Leeds businessman said yesterday.
"We all thought he had gone to continue his education. I thought he just wanted to improve his pronunciation.
"It wasn't him. It must have been forces behind him."
British intelligence has asked its Pakistani counterparts urgently to trace where the young Britons went, and more crucially who they met, during their study tours.
Officers need to know if the four bombers were ever there at the same time, or attended the same radical training schools.
The Pakistani authorities this week angrily denied accusations from India that terror training camps were once more thriving inside their borders.
Natwar Singh, the Indian Foreign Minister, replied that he had the photographs to prove it.
Western intelligence agencies have also long been concerned about the network of madrassas, the hardline religious schools, which have been blamed for turning out a generation of young jihadis. One institution which has been under recent scrutiny is in the industrial city of Gujranwala, which is just north of Lahore — where Tanweer was heading.
This new generation of training centres are nothing like their predecessors which were run by al-Qaeda in the years before the September 11 attacks on the US and were sited in the inhospitable mountain ranges straddling the Afghan border.
Western volunteers lived rough in the desert with hundreds of other foreign recruits and were taught to handle weapons and explosives, as well as spending hours listening to tape recordings of Osama bin Laden and other zealots.
"Today the camps are more like youth hostels," one young activist who attended a madrassa in southern Pakistan told The Times.
"Recruits don't spend hours scrabbling about on outward bound courses. It is more like being in a school room."
"Organisers don't want to turn out warriors who can strip down a Kalashnikov rifle blindfolded. They want to shape the mind, not the body.
"They want their recruits to embrace the idea of giving their lives for their cause, and doing nothing more technical than triggering the bomb they carry."
There are long periods of Koranic study but also what organisers call "the evolution of the jihad", which teaches how wars are no longer a battle between rival armies.
Heroic accounts of the lives — and deaths — of insurgents in Iraq are told to the class to instruct recruits: "We fight the enemy our way."
In some cases it is young Britons who have moved from Britain to make a new life for themselves in Pakistan who lecture their fellow citizens, "to make them feel more at ease".
"These British lecturers know how to give practical instructions like ‘don't go to well-known radical mosques in the UK as they are under police surveillance. Don't wander into bookshops which sell violent vidoes and militant literature as they too are being watched'.
"We were told, ‘Continue being an ordinary John'," the former activist said.
The bombers from the backstreets of Leeds followed their instructions to the letter.
They were always seen in baggy jeans, training shoes, short haircuts and were cleanshaven, even when they turned up at the local mosque for Friday prayers.
Tanweer's family say they cannot remember him arguing about politics. Hussain's relatives say there was nothing aggressive in his views about how British Muslims should behave.
Experts say there is little point trying to identify the groups who recruit the young Britons because nowadays they change their names and websites with bewildering frequency.
The Harakat al-Ansar group has had five names in the past two years.
The other practical problems for the security authorities is that there is such an enormous traffic of young Britons travelling to Pakistan to visit family that it is impossible for the police to keep tabs on them, particularly when the vast majority go there for entirely innocent reasons.
There are reports of new training centres springing up around Mansehra in the North West Frontier Province, though it is not known if any British volunteers have pitched up there.
Magnus Ranstorp, director of the Centre for the Study of Terrorism and Political Violence at the University of St Andrews in Scotland said: "Of course there are still training camps.
"I don't think you can find fully-fledged training camps in Pakistan or even Afghanistan on the same level as we had before.
"But there are many remote areas, many places where the lack of governance can provide excellent training ground. It can be done in underground shelters, abandoned houses. You don't need large facilities."
Some Pakistani-based militant groups are reported to still scout for recruits at mosques among Muslim communities in Britain.
Smaller British mosques have their own links with madrassas in the Punjab and other regions of Pakistan though they insist these are genuine schools of Koranic study, not terror training camps.
Well known militant groups, lsuch as Jaish-e-Mohammed, Lashkar-e-Taiba and Harkat ul Mujahideen have operated openly in the past and in some cases with the military's support, and boasted of their British recruits.
Mohammed Bilal, a Briton who was associated with Jaish-e-Mohammed, was the UK's first suicide bomber when in Christmas Day 2000 he rammed a vehicle packed with explosives into an Indian military post in Kashmir.
Officially, the Pakistan government — a key ally of Britain and the US in the war on terror — insists they have eradicated the culture of terror camps inside their borders.
The experiences of Shehzad Tanweer and Hasib Hussain tell a different story.
BRITISH SUICIDE BOMBERS
Asif Hanif, 21, from Hounslow, West London, mixed with radical muslims at university in Damascus, where he joined Hamas. Detonated a suicide bomb in Mike's Place in Tel Aviv, killing three people
Omar Khan Sharif, 27, from Derby, was Hanif's accomplice but failed to detonate his bomb and was found dead in the sea a week after the attack. Had also joined Hamas in Syria
Richard Reid, 32, from Brixton, South London, attended an al-Qaeda training camp south of Kabul in 2001 before attempting to light explosives in his shoe during an American Airlines flight from Paris to Miami in December that year
Sajid Badat, 25, a former grammar school pupil from Gloucester, travelled to Pakistan and Afghanistan in 2002 and attended the same training camp as Reid. He abandoned his plan to detonate a shoe bomb, but was arrested and the explosive device was found in his parents' home
Idris Bazis, 41, French Algerian who lived in Moss Side, Manchester, blew himself up in a suicide operation in Iraq in February
Wail al-Dhaleai, 22, was born in Yemen but lived in Sheffield for three years after claiming asylum in 2000. He died in a suicide attack on US troops in Iraq