By Bernard Gabony
South Asia editor, BBC News website
Suspicions that at least one of the alleged London suicide bombers may have been radicalised while in Pakistan raises questions once again about religious extremism there.
Some Islamic seminaries - madrassas - still breed extremists
Most analysts agree that the London bombers - three of whom police say were Britons of Pakistani descent - were probably trained by "minders" far more experienced in the use of explosives.
UK investigators will be keen to know if the London bombers had been trained at any time in Pakistan or neighbouring Afghanistan.
The family of one of the suspected bombers has confirmed that he studied religion in Pakistan, although it is not clear that he went to one of the Islamic schools which have been accused of fostering extremism.
The path to Pakistan is one that has been taken by many high-profile extremists.
Omar Sheikh (above) is in a Pakistani jail for the kidnap and murder of Daniel Pearl
Richard Reid serving a life sentence in the US for trying to blow up an airliner
Saajid Badat found guilty in the UK of conspiring with Reid
British-born Omar Sheikh is currently languishing in a Pakistani jail after being found guilty of the kidnapping and murder of US journalist Daniel Pearl in Karachi.
Before that Omar Sheikh had fought in Bosnia and Indian-administered Kashmir.
Recent evidence indicates he was also the mastermind behind assassination attempts against Pakistani President Pervez Musharraf.
UK national Richard Reid was sentenced to life in prison in the United States in 2003 after being found guilty of trying to blow up an airliner with explosives hidden in his shoes.
Investigators believed he received training in Pakistan and Afghanistan in the late 1990s.
Then there is Saajid Badat, raised in Gloucester in the west of England. He was found guilty by a UK court this year of conspiring with Reid to blow up the airliner.
"I have a sincere desire to sell my soul to Allah in return for paradise," he said in a letter to his family, believed to have been sent from Afghanistan.
Proliferation of militants
The spawning of a network of Islamic militant training camps in Afghanistan during the fight against Soviet control there and, later, during the rule of the hardline Islamic Taleban has been well documented.
Pakistan has tried to rein radicals in but with little apparent success
So too the role the CIA played, hand-in-hand with Pakistani intelligence services, in training and arming anti-Soviet fighters.
The unwanted spin-off for Pakistan was that areas of the country became awash with guns and saw a proliferation of different militant groups.
The unwanted spin-off for the West was that Pakistan became a country where it was easy for militants to take refuge and get backing.
What is less clear is how much all this has changed since President Musharraf threw in his lot with the United States after the 11 September attacks and declared war on extremists within.
There is little evidence that his attempt to rein in extremists in Islamic schools (madrassas) has worked.
"I want to go back and fight the Americans, I can't wait anymore," was the typical comment of a madrassa graduate to the BBC well after Gen Musharraf's stated clampdown on them.
Banned militant groups have tended to reappear under different names.
On the other hand substantial numbers of suspected militants have been captured or killed by the security forces, particularly in the wake of the assassination attempts on Gen Musharraf towards the end of 2003.
President Musharraf's government maintains that it is unrelenting in the fight against Islamic extremism. But others are not convinced.
The fight against Soviets spawned a network of militant camps
In recent weeks the head of the CIA and the US ambassador to Kabul have come as close as they can to saying that Osama Bin Laden is sheltering in Pakistan, without actually saying the words.
The ambassador was furious when a Pakistani TV station interviewed the man believed to be running the Taleban's resurgent fight against US-led forces in Afghanistan.
The interview took place inside Pakistan, but the TV station has been tight-lipped about the exact location.
Most analysts believe it was carried out in the southern city of Karachi.
So critics will argue that the networks supporting extremists are still alive and strong in Pakistan.
Wednesday's revelation by Interior Minister Aftab Khan Sherpao that his country supplied information to the UK government which helped prevent an attack in the UK before May's general election will do little to dampen that view.