LONDON — The four suspects in the London suicide bombings were young men who had lived outwardly normal lives in the northern English city of Leeds.
That leaves police, politicians, Britain’s 1.7 million Muslims and a nation known for its multicultural tolerance asking the same anguished question — what turned these young men into killers?
Just hours before heading south to London with two of the three fellow suspected bombers, Shahzad Tanweer, 22, had played cricket, his favorite pastime, and kicked around a soccer ball on the local sports field.
The previous evening, Tanweer, who had been studying sports at college, had greeted friends cheerfully as he drove his brand-new red Mercedes-Benz.
The car had just been given to him by his adoring father, Mohammed Tanweer, who immigrated to Britain from Pakistan 30 years ago.
Sometimes, Tanweer would help out at his father’s successful fish-and-chips shop, serving behind the counter or supervising the cooking.
His uncle, Bashir Ahmed, who runs a local kebab shop, was baffled and distraught at his link to the bombings.
“I saw him grow up,” Mr. Ahmed recalled, as his wife sobbed. “He was a very decent person. His family is broken. I don’t think we can survive here much longer.”
Even more baffling for security services, local community leaders, friends and neighbors is that the men had shown no obvious outward signs of planning any form of violence against anyone.
In hindsight, however, there were some telltale signs recently. One was a sudden increase in their religious observance, with two of the bombers spending much more time in a local mosque.
Tanweer is thought to have studied for at least two months at a madrassa in Pakistan, one of thousands of hard-line Islamic schools that proliferate in that country, many of which propagate a violent view of Islam.
Then there was the tall, soft-spoken bomber, Hasib Hussain, 19, who appears to have intensified his commitment to Islam two years ago. His father had sent him to Pakistan in recent months to try to improve his problematic behavior.
Another bombing suspect, Mohammed Sidique Khan, 30, had recently arrived from Pakistan, but had married a local girl whose mother was given an award by Queen Elizabeth II for her services to the community as a teacher.
Khan had an 8-month old daughter.
The fourth bomber, who killed more than 20 people in the bloodiest of the train blasts, had lived near Khan, but had moved south to Luton last year. He apparently had a girlfriend in the town — not a pattern usually associated with Islamic extremists.
Police suspect that he brought the bomb material to the three other men when they arrived in Luton from Leeds.
From there, the four traveled together the short journey from Luton to Kings Cross station in central London, each carrying a military-style rucksack and dressed in sports clothes.
In an effort to blend in more, one of the bombers had dyed his eyebrows and eyelashes brown, according to a friend, who thought it odd at the time.
In cosmopolitan London, no one was the least bit suspicious, even when, as closed-circuit television cameras later showed, the four men huddled for a while in Kings Cross station before they went their separate, murderous ways.
Three climbed aboard trains. The fourth, finding his allotted train canceled, was herded out of the station soon after his co-conspirators’ bombs exploded, stepped aboard a bus and died along with 12 others less than an hour after the other three.
Carrying paperwork with them, they might have wanted their identities to be discovered, presumably to gain credit in the eyes of their fellow radicals, security sources speculated.
“The mosques have failed to give young people proper guidance, because the imams who come are often ill-educated and often hardly even speak English,” said Zaki Badawi, a prominent moderate Muslim leader.
“It opens the way for the radicals to come in, and big money has been spent by front organizations,” Mr. Badawi said.
A Muslim university student leader, Jamal Jayyal, said the young men would have become frustrated by a serious generation gap while also feeling like outsiders in mainstream British society.
That could turn dangerous under radical exploitation, coupled with “an underlying ignorance of their own religion, and an absolute ignorance of how to conduct political dissent,” Mr. Jayyal said.
He also said there is a high unemployment rate among Muslim youths, leading to alienation and anger.
A Muslim psychologist argued that radicals could influence people feeling alienation by giving them strong personal attention and raising their self-esteem and sense of importance.
But all these theories still do not explain why Tanweer and the others were willing to kill — and to die.