LONDON - Moazamm Begg spent more than two years at the prison camp in Guantanamo Bay, Cuba, where some fellow detainees were British-born Muslim radicals or self-proclaimed al-Qaida operatives - the same sort police believe carried out last week's suicide bombings in London.
During his imprisonment, Begg got to know Muslim extremists who spoke of their anger at the United States. Some talked of attacks. Many were recruited by foreign radicals.
As members of the Muslim minority agonize over how some of their own might have caused such carnage and brace for revenge attacks, Begg - who denied U.S. allegations that he was an aide to al-Qaida leader Osama bin Laden - offers a glimpse at the possible motives.
Racism in Britain, non-assimilation in some communities, and anger over Iraq, Afghanistan and the U.S. prison at Guantanamo might have been factors, the 37-year-old of Pakistani roots says, six months after being released from the camp in Cuba. Britain negotiated his release along with that of three other British nationals.
Like many Muslims, Begg says he grew up in ethnically diverse Birmingham- England's second-largest city - pulled between Britain and Pakistan.
"I talked to many people who were self-declared members of al-Qaida while I was in Guantanamo, and there's definitely indoctrination taking place in a lot of communities in Britain," Begg said from London.
Begg described racism he encountered while growing up in the 1980s. Some of his Pakistani friends were beaten up by skinheads, he says: "Almost everyone back then was harassed at some point for being dark-skinned, for being Pakistani."
But the divide between Muslims and non-Muslims was more acute in regions such as West Yorkshire, which includes Leeds, the northern city where at least three of the four suicide bombers in the July 7 attacks are believed to have grown up. The fourth is believed to have been Jamaican-born.
Unlike Birmingham, Begg said, pockets of West Yorkshire are dominated by immigrants from specific regions. Many of the groups have not assimilated into British culture, making it easier for radical recruiters to deepen the divide and fan hatred, he said.
The neighborhood where the three suicide bombers are thought to have come from in Leeds - 185 miles north of London - is largely Pakistani.
Begg says many Muslims living in Britain have been recruited by Pakistani groups to study and fight in Kashmir, a Himalayan border region that both India and Pakistan claim.
"Just like the military doesn't recruit the old, these groups know to go after the young," Begg said. "They're stronger fighters; they're more impressionable."
Begg says other issues have also fueled hatred in the community - particularly the issue of the prison in Guantanamo.
"That is the one issue that has unified the Muslim community recently," says Begg, who is unemployed but working on a book about his time in Guantanamo. "Even though there are people from more than 40 countries there, most of them are Muslim and that's what people talk about."
More than a dozen cases of abuse and mistreatment have been documented at Guantanamo Bay, including details of a military investigation reported last week where interrogators forced a detainee to wear underwear on his head and attached a leash to his chains.
Another Briton who was jailed at Guantanamo Bay - Feroz Abbasi, who grew up in Croydon, south of London - wrote in his melancholy memoirs penned in prison that he battled shyness, loneliness and suicide attempts before discovering Islam on a backpacking trip through Europe.
In the biography are clues to how the young bombers in the London attacks could have turned violent.
Abbasi writes that he read books about Islam and jihad, or holy war, and joined an activist group - S.O.S., or Supporters of Sharia, the strict Islamic law - at Finsbury Mosque, one of London's largest mosques. Meetings at the mosque left him with fliers describing the plights of Muslims in Chechnya. He later became interested in the Taliban's fight in Afghanistan.
Although Abbasi admits training as a militant in Afghanistan, the Briton denies being an al-Qaida member.
"One thing is clear: they [the bombers] were motivated more by hatred than the faith of Islam," said Inayat Bungalwala, spokesman for Muslim Council of Britain.
Begg says it doesn't stand to reason that Muslim suicide bombers would strike Britain, a country with a high-profile Muslim population where religious and cultural freedoms have been enjoyed to a greater extent than in any other Western country.
"I was religious but it never caused me to feel like I had to carry out attacks," says Begg. "It appears that the lines are being redrawn with the targeting of civilians who had no apparent loyalty to the country where they lived. ...
"What I, and what other Muslims, struggle with is the question of why anyone could carry out these attacks in a country where we have so much freedom. Unfortunately, I think the attacks will have a profound effect on the Muslim community in Britain before that question is ever really answered."