HIGH WYCOMBE, England—An extraordinary clutch of white jihadis groomed in the suburban commuter towns northwest of London have traveled from Britain to join the terrorist militias of Syria, Iraq, and East Africa over the past decade.

The devastated family of one of these radicalized converts is now demanding to know why Britain’s security services continue to allow this to happen.

Six years after 21-year-old Thomas Evans—who was already on the authorities’ radar—was allowed to slip through a London airport en route to join al Shabaab in Somalia, his family say they have never been approached by intelligence-agency officials who might have been able to crush a growing problem of jihadi recruitment centered around High Wycombe, the mid-size suburban town where the Evans family lives.

A dozen young men are feared to have joined ISIS from Wycombe in the past few years. Three of the men accused of planning the trans-Atlantic liquid bomb plot—which changed global air travel forever in 2006—were based in the town, including a white friend of Evans, who was acquitted. The British press has taken to describing these relatively unusual converts as the white jihadis.

Micheal Evans

Samantha Lewthwaithe, a notorious al Shabaab fighter known as the White Widow, lived less than 15 miles away with her husband, one of the 7/7 bombers who killed 56 people in Britain’s most deadly Islamist terror attack. Another white convert to radical Islam, Jack Letts—dubbed “Jihadi Jack” in the British press, ran away to Syria from Oxford, which is just 25 miles to the west.

“There’s no doubt about it, there must be a network,” Thomas’s brother Micheal told The Daily Beast. “They are no different to gangs, and they’re not that smart. All the authorities have to do is connect the dots—and it just seems like they didn’t.”

Thomas Evans was prevented from boarding a flight to Kenya on a one-way ticket in 2011. When he got back home, he told his family that he had been questioned for five hours by men in plain clothes who seemed to know everything about him—his favorite fast-food restaurant, his friends, his mosque, the gym he attended, where he stayed when he took regular trips out of town, and the fact that he had just sold his car.

“Looking back now, he must have been a person of interest from what they knew about him. It sounded like round-the-clock surveillance,” said Micheal.

And yet the authorities made no effort to contact the family. Thomas and Micheal’s mother, Sally Evans, is adamant that she would have stopped her eldest son from joining the terrorists if she had been tipped off by the security services.

“Of course, I would! I’m his mother,” she told The Daily Beast. “I’d have taken his passport, gone to the police, anything—sat on him if necessary.”

Instead, unaware of how deeply he had been radicalized, she accepted his wishes when he said he was going to Egypt for a few months to take an Arabic course. Once he got to Cairo, however, Thomas Evans began an overland journey that eventually took him into Somalia, where he was to become a notorious al Shabaab fighter who beheaded Christians and took part in murderous cross-border raids. He was killed by a Kenyan sniper in 2015.

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Walking along Wycombe’s High Street on a bracing night this week, Micheal Evans was in reflective mood. He pointed to the church walls and car park ramps where he and Thomas would practice jumps and grinds on their BMXs. As they grew older, they went to see bands in the bars in town and sneaked the odd underage drink. As well as his big brother, Thomas was Micheal’s best friend.

Micheal Evans

Thomas was also likely to get into scrapes. At 6’2” and a regular gym-goer who took up amateur boxing, he fancied himself in a fight and would often return home from a night out with blood on his favorite white sweater. He eventually graduated from these fights to some petty crime and involvement with local gangs.

It therefore came as a relief to his family when he converted to Islam, stopped drinking, and seemed to find peace.

What happened over the next few years was a gradual process of radicalization. Micheal and his mom noticed that he was becoming more and more focused on religion, but they did not recognize the warning signs that their beloved Thomas was morphing into a Salafi extremist.

After he moved to a new mosque—the Muslim Education Center—he stopped listening to music, refused to eat from the family’s non-halal pans, would lecture them incessantly for watching TV, or with anti-Western political rants. He started wearing a long Arab-style tunic called a thobe.

“Mum used to say: ‘You’re not going out of the house wearing that,’” said Micheal. “And he would change when he got out.”

He used to wear his trousers rolled up, which is a Salafi affectation in honor of the Prophet Muhammad. During his last Christmas in England, he went to stay in Burnley with friends he had met via people from the mosque, in order to avoid the decorations and celebrations in the family home.

In retrospect, the most obvious sign that Thomas had strayed beyond the realms of normal behavior was when he returned from one of his regular trips to Burnley—a town with a large Muslim minority—having been circumcised.

“Essentially, he had an operation in somebody’s house!” said Micheal. He was bed-ridden for weeks with an infection and the family convinced him to seek proper medical help. “The doctors were shocked to say the least. It was not done right, it was not clean.”

The Evans family did not feel as though they knew enough about Islam to challenge these increasingly extreme views, and that is one of Micheal’s motivations in helping to set up a new organization with a helpline and website that will be able to connect families with moderate imams and offer guidance on spotting the signs of radicalization.

At one point, Thomas invited another white Muslim convert round to the family’s home in the suburb of Wooburn Green to try and reassure his mother. That man was Donald Stewart-Whyte, his father was a Conservative Party activist and his half-sister was a well-known model.

“He sat on my kitchen floor,” said Sally Evans, gesturing to the back of the house. “And told me Thomas was a good Muslim, that he was doing well.”

When Stewart-Whyte left, Thomas asked his family what they thought of him. “We said he seemed all right,” said Micheal. “Tom said, ‘Well, he was charged with terrorism offenses’—and we were like, ‘Why are you with someone like that? Why would you bring him here?’ Tom said he was innocent.”

At trial, Stewart-Whyte was acquitted of conspiring in the liquid-bomb plot to bring down trans-Atlantic flights that would have killed hundreds of people in the biggest terror attack since Sept. 11, 2001. He pleaded guilty to possession of an illegal firearm, ammunition, and a silencer.

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Stewart-Whyte and two of the plotters who were convicted, Assad Sarwar and Umar Islam, had attended Thomas’s mosque, which is located at the back of a rundown store selling Islamic literature on one of the shabbier roads in Wycombe.

A spokesman for the Muslim Education Center, Jaleil Raja, denies that Thomas Evans—or anyone else—was radicalized at the mosque. He said he had been a worshipper at the center for well over a decade and claims Thomas was never a regular, a contention that is strongly disputed by the Evans family.

Raja said that “definitely no one was proud” that so many members of this small Muslim community had become involved in terrorism.

Another regular at the mosque told The Daily Beast that there were mixed emotions about people going to fight abroad.

“There’s always two sides to every story. The media tells the bad side of ISIS. If I want to hear the other side, I’d probably have to go out there,” said one man who did not want to be named. “These guys have gone but you have to assume they are going to protect people.”

This worshipper, who said he had been attending the mosque since it first opened at the start of the century, said the teaching there had never changed despite so many members of the mosque getting into trouble with the authorities.

They don’t teach the young men about avoiding radicalization, he said. “It’s like sex education, they teach it so young in schools, and now you see stories of girls being raped by 12-year-olds. Sometimes that kind of teaching can go wrong.”

Raja agreed that there was not much in the way of anti-extremism training, but he said that anyone they believed to be a threat would be reported to the authorities through Britain’s controversial PREVENT counter-radicalization program.

The most recent Muslim Education Center worshipper who traveled to Iraq and Syria is Shabazz Suleman, 22, who was a student at the prestigious Royal Grammar School in High Wycombe. He says he slipped away from a family vacation in Turkey in 2015 before crossing into Syria to join ISIS. Once there, he says he spent his time riding bikes and playing PlayStation games, a claim that worshippers at the mosque seemed to take at face value.

Suleman’s father was said to be horrified about what had happened and has no idea how his son became radicalized.

Raja denies Evans family suspicions that the mosque could have done more to alert them to their son’s state of mind, but he agrees that being tipped off by the authorities would have been hugely beneficial. “It does seem bizarre if they were aware of him,” he said. “I would definitely want to be told so I could be firm with my son.”

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Micheal Evans

Micheal and Sally will always believe they could have done more to stop Thomas, and they are battling to come to terms with the fact that a member of their family became a monster. In one of the raids carried out by al Shabaab, Thomas is described as forcing Christian villagers to kneel in the street before cutting their throats with a knife.

He was eventually killed by a Kenya security official during a failed raid across the border in 2015.

“It's so weird, how someone who’s grown up as your own flesh and blood could do that to somebody,” said Micheal. “It doesn’t make any sense, I don’t think it ever will make any sense. I’m glad he’s not around to hurt anyone. It’s like his soul was gone.”

For five years, Micheal worked as a professional photographer but he has now quit to concentrate on the battle that has consumed him ever since his brother became a terrorist. “One of the ways I get through it is to take what I’ve been through and use it. There’s no point in wasting that,” he said.

Micheal has joined the counter-extremism organization Faith Matters to head up a new project, Supporting Affected Families from Extremism (SAFE). He will answer calls on a helpline set up to provide long-term support to families who have already lost a relative to extremism, or advice for parents who fear their child is being radicalized.