The play was called Don’t Judge Me, a satire that poked fun at tabloid stereotypes of British Muslims. It was written, directed and produced by a 15-year-old from Brighton named Amer Deghayes, who had taken inspiration from some of the less considered headlines of the Daily Mail and the Sun. “They were so ludicrous they made me laugh,” he told one of the adults who helped with the production. “The way they called young people feral, wow!” The play, which was set to a rap soundtrack performed by Amer’s own group, Blak n’ Deka, toured theatres on the south coast in 2010, winning awards and plenty of plaudits.

Amer, who had his sights set on becoming a serious journalist, was the eldest son in his family. Two of his brothers were twins, Abdulrahman and Abdullah, a year younger and both keen footballers. Next was Jaffar, a studious, slight 13-year-old who had always wanted to become a fireman. The brothers bonded through kickabouts in their local park and swimming, running across shingle beaches headfirst into the English Channel. On Facebook, pictures show a grinning Amer pretending to swallow a starfish beside Brighton pier.

When he wasn’t spending time with his family, Amer hung out with his best friend, Ibrahim Kamara, a refugee from Sierra Leone. They did everything together, often writing rap tracks and politicised film scripts. Their last joint project was to have been a documentary exploring the insecurities of adolescence, titled Me, Myself & Before. In a fundraising pitch from November 2012, Amer and Ibrahim wrote: “It is a time in life when we are uncertain of the future, when some feel different, isolated and lonely. Teenagers are often confused and feel like outcasts.”

Their request for funds was made by Cultures Club, a Brighton youth arts organisation, and approved by the Heritage Lottery Fund. But by the time the funding was confirmed in the summer of 2013, it was too late – Cultures Club had lost all contact with Ibrahim and Amer.

In fact, in October 2013, Amer left Brighton for Syria, where he joined a radical Islamist militia fighting Bashar al-Assad’s army. Ibrahim soon joined him, along with two of Amer’s younger brothers, Jaffar and Abdullah. Two years later, only Amer is still alive.

The young men left behind a large group of friends in Brighton, many of whom also appear to have been radicalised. Among them, police identified at least 20 people they deemed likely to travel to Syria; most of them were under 18, and at least half were converts from non‑Muslim backgrounds. Together, these teenagers so alarmed the authorities that Brighton’s senior police officers and council chiefs held secret meetings in early 2014 to discuss the possibility of a terror attack from its residents – and the seaside city was placed on the register of areas requiring extra support under the government’s counter-extremism strategy.

The question of what motivates young British men and women to leave their homes and join jihadist groups fighting in Syria has been the subject of heated public debate. The prevailing orthodoxy cites Islamist ideology as the principal driver – and it is obviously a necessary element, if not always the predominant motivation. What has been less understood is the process by which young people grow alienated with their own country, and seek the validation of their identity in a faraway civil war.

The story of Amer Deghayes, his brothers and best friend provides unusual insight into the radicalisation of young men

Based on detailed testimony from family, friends, police, social services and counter-terrorism officials, the story of Amer Deghayes and his brothers provides unusual insight into the radicalisation of young men in Britain. Their journey from the south coast to Syria cannot be reduced to a single factor, but it involves racist abuse, allegations of police neglect, and the collective failure of numerous authorities – both those charged with protecting vulnerable young people, and those charged with preventing radicalisation.

Their story echoes what we know of the young European Muslims involved in the recent terror attacks in Paris and Brussels – namely, a culture of delinquency that evolves into extremism, as well as a connection between radicalised siblings. It poses a difficult question about integration in Britain: if multiculturalism is faltering in what is regarded as one of the UK’s most liberal cities, then what hope is there for other places? Above all, it confirms how poorly we understand what drives young Britons to the battlefields of Syria.

In the summer of 2008, the Deghayes family arrived in Saltdean, a coastal village a few miles east of Brighton’s city centre. They had spent the previous two years in Libya with their extended family, who lived a comfortable middle-class existence in Tripoli. But Amer’s mother and father, Einas and Abubaker, missed England and decided it was time to return.

Omar Deghayes, Abubaker’s brother and Amer’s uncle, had recently returned to Brighton. Omar was arrested while living in Lahore in April 2002, and deported to Guantánamo Bay, where he was tortured. One incident, in which a US guard violently attacked him, left Omar blind in his right eye. Omar was never charged with any crime. According to his lawyers, the US had initially identified him as a jihadist who had fought in Chechnya, and said it had videotape of him brandishing a Kalashnikov. After obtaining the footage, the lawyers said it was a completely different person, a Saudi jihadist who had died in 2004. (The British government requested his release, along with four other British residents detained at Guantánamo Bay, in August 2007.)

Abubaker and Einas wanted to build a new future in Saltdean. Amer and the twins, Abdulrahman and Abdullah, were sent to Longhill High, a school whose pupils came from some of Brighton’s most deprived areas. According to family friends, the Deghayes boys, who were among a tiny minority of Muslim pupils, were mercilessly targeted. Taunts of “Paki” and “terrorist” followed them around the playground. In one incident, students poured water on the twins in the canteen. Saltdean Oval, the park where the boys played football on summer evenings, soon became a place they feared.

Facebook Twitter Pinterest The Deghayes family live in Saltdean, near Brighton, East Sussex. Photograph: Andrew Hasson

Over time, the attacks escalated. Anti-Muslim graffiti was painted on a seafront promenade in Saltdean only 200m from the Deghayes family home. On 1 June 2009, according to police logs, the words “Behead all Muslims” were daubed in foot-high capital letters beside beach huts that lined the coastal path. As soon as council workers scrubbed away the words, they would reappear.

The threats were not merely the work of local kids. Sussex police had received intelligence that the neo-Nazi National Front had set up a chapter in Saltdean in order to target the Deghayes family. “Other organised rightwing groups were also believed to have targeted the family,” the logs stated, citing the anti-Muslim English Defence League and Casuals United, a network of far-right football hooligans, who view themselves as a “ready-made army” against radical Islam. Both groups invited similarly minded individuals to target the family’s Saltdean home, publishing the “addresses of the mosque [that the family attended] and homes on rightwing websites with a call for action”, according to a police intelligence assessment.

Police logs documenting a single month, September 2009, reveal the extent to which the family was targeted. On 3 September, the windscreen of the Deghayes’s family car, parked outside their detached home on Arundel Drive East, was smashed. On 7 September, the twins, Abdulrahman and Abdullah, were racially abused at school and the perpetrators were overheard insulting the boys’ mother. (The twins retaliated violently and were suspended.)

Less than a week later, Einas was travelling on the number 27 bus from Brighton with Amer and his brothers when a group of youths surrounded them. Leaning towards the family the mob made throat slitting gestures and told them: “You are dead.” On 11 September, shortly after nightfall, a large group of youths congregated in the front garden, hurling bottles, bricks and stones at the house, smashing the dining room window. On 14 September, one of the twins received anonymous threats on Facebook and the Deghayes’s house and car were attacked again. On 22 September, when walking home from school, the twins were ambushed by a group wearing balaclavas. During the assault, Abdullah was stamped repeatedly on the head and kicked in the ribs.

The police record for the month of September 2009 ends there – but there is an addendum stating that the family “did not report many other incidents during the same month”.

Across Brighton, Amer’s best friend, Ibrahim Kamara was enduring his own nightmare. He had arrived in Britain with his mother in 2004 as a refugee from Sierra Leone. When he was one year old, anti-government rebels from the Revolutionary United Front had attacked their village outside the capital, Freetown. “I picked my baby up and we ran for our lives. Violence is not a joke to me. I’ve lived it, I’ve seen what it can do,” Ibrahim’s mother Khadijah told me when we spoke earlier this year.

Ibrahim met Amer at al-Quds mosque on Dyke Road in Brighton, where Amer’s father was an influential figure. The two teenagers clicked immediately: in a milieu where toughness was valued, both were almost conspicuously laid-back; they brushed off the taunts of racists and bullies, and were regarded as likable popular boys. Plus, they were considered decent rappers – among the best of their peers. “They were well-liked, funny guys,” said their friend Tommy Simmons, now 19. “Ibrahim made everyone laugh, someone who made you feel better.” When he wasn’t rapping, Ibrahim helped his mother out at her charity shop, Strive in the Name of Allah, on Lewes Road in Brighton.

In the spring of 2010, Ibrahim was savagely beaten on the streets of Bevendean, north Brighton. According to his mother, the father of a teenager who had earlier made racial taunts against her and her son “paid somebody to beat Ibrahim”. Her son was in hospital for days. “They used to call us Paki, nigger, all sorts,” she recalled.

In 2010, social services officials charged with looking after the Deghayes family concluded that racism eroded the family’s “coping capacities”. While the twins, Abdullah and Abdulrahman, became mired in daily battles with their tormentors, Amer kept his cool. “My position, even with the racism, was to deal with such things in a non-violent way. I didn’t let it affect me, I didn’t let it bring me down,” he told me in an interview earlier this year.

The family sought protection from the police. During the sustained attacks on their home in 2009, seven arrests were made but no one was charged. Other incidents of alleged racist abuse involving the Deghayes boys were not pursued by the Crown Prosecution Service, in some cases because of insufficient evidence, and in others because they were not considered in the public interest.

In March 2010 the twins, Abdulrahman and Abdullah, told social workers they felt racism existed within the police and that not enough was done in response to their reports of harassment and antisocial behaviour. They felt their reports were “not investigated”. Jackie Chase, a friend of the family, told me: “The authorities became something threatening rather than supportive.” In 2010, the boys’ father, Abubaker, told police that “his sons were being radicalised by the lack of police activity about the complaints”.

Sussex police does not divulge dealings with individual members of the public but said that it investigated all complaints against the force. However, it would not be until the end of 2011 that the force arranged for a non-white officer to meet the Deghayes boys and officially discuss why they felt the police had treated them unfairly.

Subject to sustained racism and uncertain whether they could trust the authorities, the Deghayes boys must have been tempted to retreat into the stability of the family home. But life within the whitewashed walls of their detached house in Saltdean was far from serene. For years, the police received allegations that the family had also endured the violent temper of Abubaker. Reports of the conflict within their home surfaced again in November 2010 when a concerned third party contacted a charity for help.

As the authorities investigated, further allegations emerged, including one that Abubaker had whipped his sons with electrical cables. Scarring and numerous bruises were reportedly identified on the children’s backs. Abubaker strongly denies these allegations.

Amer Deghayes on Brighton beach. Photograph: facebook

On 23 November 2010, at a child protection case conference, social workers, police and healthcare workers concluded that Amer, Abdulrahman and Abdullah, and Jaffar, “were subject to actual, emotional and physical harm”.

Although the officials drew up child protection plans for the boys, it seems that the authorities again failed to effectively protect them. Abubaker was arrested and subsequently released. His stringent bail conditions prohibited him from visiting the family home, and even Saltdean itself. Yet the father “persistently broke” his bail conditions and continued to visit the boys, according to the police. During one visit Abubaker allegedly prevented calls for help by disconnecting the landline.

Eventually, the boys retracted their initial statements against their father and no charges were brought. “The children provided letters withdrawing their support for a prosecution. They [later] told police that they had been told what to write by Abubaker,” according to police logs.

Abubaker has always strenuously denied any acts of violence against his wife or his sons. He says such allegations were part of a racist vendetta propagated by his enemies.

For Amer and his brothers, the cumulative impact was profound. The council’s team for helping troubled families believed that the boys had suffered “significant emotional abuse”. Their alleged exposure to violence was considered so deleterious that they might have suffered “symptoms of post-traumatic stress”.

In early February 2011, Einas and her sons fled Saltdean for Brighton. Their emergency accommodation, in Preston Drove, was a Victorian maisonette among the neat rows of suburban terracing near Preston Park. The house, supplied by the council, was riddled with damp, and water dribbled down the wall when it rained. It was so draughty that the heating costs helped push the family into debt.

One official from the council’s Integrated Team for Families, who made a routine visit in March 2011, described a wretched scene. The entire family were ill in their beds. “The house was freezing and water was leaking from a ceiling light socket on Jaffar as he tried to sleep in his sodden bed.”

The family continued to suffer racist abuse, according to social services, as did Ibrahim Kamara and his mother Khadijah. In total, Khadijah says she was forced to move her family 11 times over six years after being targeted by racists. “We had to move to a place in Seaford where there was no fridge, no kitchen. My kids and I had to live on junk food,” she told me last December. For eight weeks in 2013, Ibrahim and his mother slept on the floor of her charity shop. “Having to move because of racial harassment affected my children greatly and because of that it affected me,” said Khadijah.

Amer focused his energy on his studies, completing a work placement at Saltdean library. The twins, however, had started fighting back. During the spring of 2011, Abdullah and Abdulrahman won a series of street brawls against their former bullies. By the summer they had secured the respect of other troubled teenagers, many of whom were already known to the city’s social services and police.

The 15-year-old twins soon became the leaders of a gang of about 20 teenagers that was feared throughout Brighton. Abdullah mugged passersby for mobile phones and shoplifted. He was also investigated for an alleged violent assault on an Italian student. The southern stretch of London Road, a down-at-heel strip containing pound shops and amusement arcades, became the gang’s turf.

Amer watched helplessly as his other brother, Jaffar, 13, was sucked into the violence. Towards the end of 2011, staff from social services observed a dramatic turnaround in Amer’s brothers, who had gone from being victims to perpetrators: “The boys are enforcers/bullies across the city, looking for a belonging and ending up in gang culture.” Police at the time regarded the three younger boys as a “one family crime wave”.

Facebook Twitter Pinterest Abubaker Deghayes, whose three sons went to fight in Syria, at home in Saltdean. Photograph: Andy Hall/The Observer

By November 2011, the twins had become so notorious that the Brighton Crime Reduction Partnership, a coalition of police and council officials, agreed an exclusion notice that banned Abdullah and Abdulrahman from a large area of the city, stretching from the city centre to the marina 3km away.

With their father no longer living with them, the twins began to take control at home, inviting other members of their gang to stay with them. The new lodgers lied to Einas to exploit her kindness – telling her they were homeless and hungry. One housing official described witnessing the twins “barking orders” at their mother. Police received frequent reports of missing teenage boys, only to find them living at the Deghayes’s family home. Throughout 2012, neighbours reported loud music until the early hours, doors banging, people coming and going throughout the night.

Einas, who is described as loving and generous by those who know her, is understood to have become profoundly exhausted, looking after her own sons and the other teenagers who would come to stay in her house. Throughout this period she had one key ally: Amer. While his brothers were constantly causing trouble, Amer never came to the attention of the police. Faced with the mounting disorder, social services described him as a rock, offering unstinting support to his mother and acting as a replacement for his father by trying, with great difficulty, to put boundaries in place. This left him vulnerable and heavily outnumbered: according to social workers, Amer’s brothers “bullied” and “assaulted him”.

The 15-year-old twins soon became the leaders of a gang of about 20 teenagers that was feared throughout Brighton

Observations from family liaison officials in early 2012 describe a 17-year-old fully engaged with society, blossoming at City College where he was popular, and also cementing his reputation as a skilled rapper. Focusing on his business studies course, Amer was determined to go to university. He had also started attending al-Quds mosque more frequently, along with Ibrahim; their deepening commitment to religion was viewed by social services as pious rather than doctrinaire.

By contrast, Amer’s brothers were not doing well. In their final year at Longhill, the twins rarely attended classes, although they sometimes turned up for free school meals. Staff at the school reported that they were reluctant to confront the twins, fearing that they would be accused of racism for doing so. Other pupils at the school feared “reprisals” from the gang. A spokesman for the city council, speaking on behalf of the school, said they would not comment on specific claims while they were cooperating with an ongoing serious case review by Brighton’s Local Safeguarding Children Board.

Jaffar, meanwhile, had transferred to Varndean school in north Brighton to avoid the racism experienced by his older brothers, but the same problems emerged at his new school. On one occasion, Jaffar, who was then 13, was hospitalised following a playground fight. Despite this and his involvement in the twins’ gang, Jaffar was viewed by social services as the brother most likely to escape “gang culture”. Social workers noted that he had begun to see Amer as the male role model he wanted to emulate. A school report from the 2012-2013 academic year portrayed Jaffar as a well-adjusted teenager “who is pleasant to talk to … and enjoys talking to adults”. Despite an attendance rate of just 59%, his teachers were sympathetic, aware that he was kept awake by the nightly commotion at the family home.

Nonetheless, Jaffar was eventually banished from mainstream education for violence and sent to the city’s Pupil Referral Unit (PRU), which provided special classes for “troubled” children.

Jaffar sat his GCSEs at the PRU the following June. His former teachers at Varndean had predicted that he would get at least eight GCSEs. In the end, he passed only three. “That hit him hard, being sent to the PRU had the undesired effect of alienating him from future career opportunities,” a family friend who did not wish to be named told me. “You could see the hope drain from him.”

Shortly before the 2012 summer holidays, Jaffar’s behaviour deteriorated rapidly. In July, he was arrested with one of the twins, Abdulrahman, for allegedly assaulting and robbing foreign students from the University of Brighton’s International College. Staff at the PRU were shocked, describing his violence as “completely out of character”.

Facebook Twitter Pinterest Abdullah Deghayes. Photograph: Family handout/PA

Amer offered Jaffar support, encouraging him to attend the mosque. Yet police records from this period show that Jaffar and his brothers, except for Amer, were at risk of becoming prolific offenders. In May 2012, police recorded 15 incidents with the Deghayes brothers. The twins were viewed by police as a criminal double act, skilled at evading prosecution by exploiting the fact that neither the police nor their victims could tell them apart.

Summarising the behaviour of Abdulrahman, Abdullah and Jaffar during the second half of 2012, Brighton’s Youth Offending Service concluded that “from a criminal point of view the boys have all amped up and cannot be ignored”.

During the early evening of 16 September 2012, police received reports of a teenager staggering about The Level, a small park near the centre of Brighton, where students would congregate to kick off nights on the town. It was Jaffar. Clearly drunk, the 14-year-old was in an aggressive mood, yelling sexist abuse and threatening passersby. “Allah will seek his revenge for me,” the teenager yelled to a crowd that had formed around him. “Do what you want to me. See what happens when judgment day comes. You will all go to hell.”

Police officers seem to have dismissed his tirade. Jaffar’s outburst does not appear to have been referred to the Prevent programme – the principal strand of the government’s counter-terrorism strategy, which is intended to stop people being drawn into radicalisation and violence. (Despite presiding over a population of 275,000, Brighton and Hove city council only employs one full-time member of staff to work on Prevent.)

There is little hint that the authorities believed the Deghayes boys were at risk of becoming radicalised – even though allegations had been made to police in 1997 that their father, Abubaker, had been preaching in a manner that might “incite racial unrest” and “reflected strong al-Qaida sympathies”. Abubaker has strongly denied these claims.

More recent, and more obvious, was the experience of the boys’ uncle, Omar, at Guantánamo Bay. In an interview earlier this year, Amer cited Omar’s mistreatment in prison, and his uncle’s first-hand accounts of the brutal injustices of the Bush administration’s reaction to 9/11 – backed by British complicity – as having first planted doubts in his mind about life as a Muslim in the west. “The war on terror was obviously a war on Muslims, the Islamic way of life,” Amer told me.

Facebook Twitter Pinterest Ibrahim Kamara was killed in Aleppo. Photograph: internet

In January 2013, the first meeting in Brighton of Channel, a Home Office initiative designed to protect vulnerable people from being drawn into violent extremism, was held. The month before the Channel meeting, Amer’s father travelled from Brighton to northern Syria with an aid convoy, although, at that time, travelling to help the Syrian people cope with its brutal civil war was uncontroversial. The Deghayes boys do not appear to have been discussed at the Channel meeting.

The following month, February 2013, one of Jaffar’s friends, a Muslim teenager who I will call Kadeem, was spotted by staff at Varndean school leaving the school’s prayer room during lunch. The teacher noticed something odd: Kadeem was accompanied by two pupils who were not Muslim. The pair were reminded that it was forbidden for non-Muslims to use the facility. Kadeem stepped forward and explained that he had converted them and was teaching them how to pray.

The teacher listened as Kadeem ran through a long list of names of friends who had recently converted and who, he said, “will all go to heaven and be safe”. Amer, he told the teacher, was his right-hand man, tasked with ensuring that youths attended al-Quds mosque. Kadeem, who became increasingly animated throughout the conversation, also showed the teacher video footage on his mobile phone of what he said were “Jews attacking Palestinians”.

Alarmed, the teacher contacted the council’s community safety team. However, it is understood that community safety officials told staff that they had no concerns regarding al‑Quds mosque, adding that the school should remember that Amer was the “sensible one of the family”.

During the first half of 2013, social workers began to hope that Jaffar, who was now 16, was starting to settle down. He began taking Arabic classes at the weekends, and in his spare time he watched religious lectures on his laptop. In the summer he observed Ramadan voluntarily for the first time.

As Jaffar became calmer, Amer was becoming increasingly agitated by the war in Syria. A decisive moment came on 21 August 2013, when Assad’s forces fired rockets carrying chemical weapons into the crowded suburbs to the east of Damascus, killing hundreds. A few hours later, footage appeared online of children frothing at the mouth, their skin blue. “I saw the chance in Syria to help and a chance to remove [Assad’s] secular Ba’athism,” Amer told me. “I don’t want to be the person standing on the sideline and watching.”

Facebook Twitter Pinterest Omar Deghayes was imprisoned in Guantánamo Bay for more than five years and subjected to torture that left him blind in his right eye. Photograph: Teri Pengilley

Shortly after, Ibrahim’s mother Khadijah remembers her son mentioning Syria for the first time. It was a lunchtime towards the end of August 2013, the end of the school holidays, which Ibrahim had mostly spent with Amer, getting fit in the gym and praying at the mosque. Khadijah recalls Ibrahim and Amer talking animatedly about the suffering of the Syrian people. “I told them you have no money, you haven’t finished school. I thought they were going through a phase,” she said.

When, on 29 August, parliament rejected UK military action against Assad to deter the use of chemical weapons, Amer’s belief that the west did not care about Muslims hardened. “He kept asking why isn’t the west helping? He saw it as a betrayal of the Syrian people, of Muslims,” said a former school friend.

Meanwhile, Jaffar, who had just returned from a brief trip to Libya to visit relatives, also seemed to have developed strong political views. In September, a youth offender officer found the teenager strikingly distant. But when the turmoil gripping Libya was mentioned, Jaffar’s mood instantly changed, and he denounced “all Americans as terrorists”. After this incident, Jaffar was referred to the Channel counter-terrorism programme.

In mid-September, when Jaffar enrolled on a sport and public service course at City College, officers on the police Prevent team contacted staff at the college to request that they “flag any concerns that they may have re radicalisation” involving Jaffar. Instead, they received reports of a popular “alpha-male figure”, who was respectful towards women and challenged peers who he felt were not.

On 28 September 2013, Sussex Police decided to wind down Operation Blower, an initiative that had been introduced six months earlier to dismantle troublesome gangs of young people in Brighton, among them the group that included Abdulrahman and Abdullah Deghayes. Senior officers deemed the operation a success, observing they found “no concerns regarding radicalisation” with any of the Deghayes boys. Around the same time, the council’s troubled families team decided to cease its work with the Deghayes family, noting that there had not been enough progress to justify keeping the case file open.

Not long after, on 15 October, dressed in black, Amer set out for Syria. The authorities had no knowledge of Amer’s journey.

It was not until the following month that police learned that Amer had left the country, and even then it was believed that he was undertaking an aid assignment. On 11 November 2013, the Prevent case management committee – including some of the city’s senior police officers, council officials and social workers – met in a terraced building near Brighton’s Royal Pavilion to discuss Jaffar. The panel concluded that he “showed low risks of being drawn into extremism”, noting that he had stopped smoking cannabis and drinking, seemingly oblivious that such behaviour might suggest a hardening of his beliefs. The panel decided that Jaffar should not be considered as a candidate for the Channel process – which could have led to his entering a deradicalisation programme.

Something crucial did emerge during the meeting, however. Social workers had heard that Amer had travelled to either Libya or Turkey on a humanitarian mission. Sussex police admitted they had not known about this, but agreed to advise the Prevent officials of any “emerging risks” emanating from Amer’s travels, a possible reference to the potential impact on his brothers.

On 3 December, police discovered a Facebook account registered in Libya, which they soon determined was linked to Jaffar. Called the Youth Empowerment Society South East Division for Islam, it contained a weblink that led to a picture of boxing apparatus labelled “The brothers gym”. Investigators identified it as the gym at al-Quds mosque. Scrolling deeper into its timeline, officers found an image of balaclaved men sitting on horseback in a desert. Fluttering in the background was a black flag adorned with white script, the “black flag of jihad”.

Syria's civil war: five years of Guardian reporting Read more

But once again no action was taken. Jaffar was never referred back into the Channel programme, while the mosque’s gym does not appear to have been investigated. Jaffar’s school, it appears, did have concerns over Amer’s “youth group”, but believed the gym was linked to criminality rather than radicalisation.

No one appeared to know that Jaffar was in touch with Amer, who had safely arrived in northern Syria and enrolled with Jabhat al-Nusra, the Syrian affiliate of al-Qaida, the most powerful Islamist group fighting Assad at that time. Speaking to Jaffar on Facebook, Amer told his younger brother that the food and shelter in Syria were better than he had expected. There were other British fighters with him, he said, and Muslims from every corner of the world. “We are part of something here, part of something bigger, trying to bring back Islam and justice to the land of Muslims,” he told Jaffar.

In the first week of 2014, an official from the Youth Offending Service described his astonishment at Abdullah’s fragile appearance. “He is very vulnerable and would always look sad and lost, like a little boy.” What the Youth Offending Service did not know was that in mid-January, Abdullah had stolen his passport from his mother’s handbag. In less than a week he would be heading to Syria. Unlike Amer, he would not be travelling alone. Jaffar, 16, was coming, along with Amer’s best friend, Ibrahim.

At this point in time, up to 500 Britons were suspected to have travelled to Syria to fight, and UK border controls were on high alert. Yet on 26 January 2014, three teenagers from Brighton – one of whom, Ibrahim, was carrying the passport of his 15-year-old younger brother, who did not look much like him – walked through Luton airport and boarded a £59 one‑way direct flight to Istanbul, the gateway city to the Syrian frontlines.

It appears that counter terrorism officers failed to inform Sussex police that they were watching the family – a notification that was only made on 14 February 2014, 19 days after Ibrahim, Abdullah and Jaafar left Britain. Vital intelligence that could have stopped the boys from travelling was never shared.

When Jaffar, Abdullah and Ibrahim arrived in Istanbul at the end of January 2014, they caught an overnight bus to Antakya, on the Syrian border. From there, a dust-streaked coach took them across the Bab al-Hawa crossing and into northern Syria. The territory they had entered was held by Jabhat al-Nusra. To join the Islamist militia the three teenagers had to prove they could speak Arabic. They also needed someone who could vouch for them. Amer paved the way.

Back in Brighton, senior police officers were stunned by the discovery that four local teenagers had gone to fight in Syria. They realised they would have to scramble to prevent more young residents from following the Deghayes brothers. According to an intelligence report, dated February 2014, “the police began to receive intelligence and calls from parents who were concerned about their children associating with the Deghayes and also their conversion to Islam and going to Syria”.

Jaffar Deghayes. Photograph: internet

Police soon discovered that a fifth young man, Mohammed Khan, had also left Brighton for Syria. In fact, he had travelled with the same aid convoy as Amer. Khan, who is from Brighton’s Bengali community, was regarded by security services as a “clean skin”, because had never previously come to the attention of the authorities. Counter-intelligence officials believe that Khan, 22, has become a senior commander in Jabhat al-Nusra, directing operations in the Idlib area.

Within weeks of learning that Ibrahim, Abdullah and Jaffar had left Britain, Sussex Police identified a group of 20 other young people – at least 13 of them under 18 – who they deemed likely to attempt travel to Syria . Many had been among the gang of runaways who stayed at the Deghayes home in Preston Park. “Extremism was like a contagion among this group of friends,” a source familiar with the case said.

On 11 March, alarmed at the prospect of two dozen radicalised teenagers in Brighton, police chiefs, community safety officials and the chief executive of the city council met “to consider counter-terrorism related to a number of young people in the city”. On 2 April – seven weeks after Jaffar, Abdullah and Ibrahim left the UK – the identities of the five young Brighton residents in Syria were passed onto the council’s head of community safety.

Two thousand miles to the east, one of them, Abdullah, was finalising combat training ahead of an al-Nusra offensive to push back pro-Assad militias near the town of Kessab in northwestern Syria. Eleven weeks after arriving in Syria, on 14 April 2014, Abdullah went into battle. He was killed by a sniper while chasing retreating enemy forces. A photograph posted on Facebook by Jaffar shows Abdullah lying on his back, in combat fatigues, eyes closed, mouth open.

Back in Brighton, Abdulrahman, still grieving from the death of his twin, was referred to probation officers on 9 June over “wider extremism concerns relating to the family”. Soon after, Abdulrahman was arrested after allegedly assaulting a couple with a knuckleduster. He was remanded to Lewes prison in east Sussex.

On 23 September 2014, US president Barack Obama announced that a cruise missile attack had targeted a cell of “seasoned al-Qaida operatives” in Syria’s Idlib province. Ibrahim Kamara was killed in one of the strikes. His mother Khadijah says that she cannot excuse her son’s actions, but she has forgiven him. “You love him, he was your child. I loved him so much, a gentle child. He’s still my son.” Amer told me: “All I can say is that her son loved her and it affected him that she didn’t speak to him much.” He rationalised his best friend’s death as the price of fighting for what they believed in. “Islam comes with a responsibility. If Islam is under attack, our duty is to help.”

The following month, the final member of the trio who had left for Syria in January was killed. Jaffar was shot by Syrian government troops during a close-range firefight amid the ruins of Idlib. He was 17.

The deaths of the Brighton boys, and the threat of more young people following in their footsteps, has prompted considerable soul-searching in Brighton. A series of meetings were held throughout 2014 between police, leaders of the city’s mosques, council officials and counter-terrorism officers. In November 2014, the council launched an awareness campaign to stop more city residents heading to Syria.

A serious case review is currently investigating the state’s interaction with the Deghayes family and is expected to be published next month. It is expected to highlight failures in communication between the police, council, teaching staff and children’s services as reasons why five young men from Brighton were able to slip through the net. “They each knew only 20% of the problem, they were making decisions without anything remotely close to the full picture,” said a source.

Others believe that responsibility for what happened should be more widely shared. “The boys were failed all the way along, by everybody,” Jackie Chase, a friend of the family, told me. “I feel the boys went to Syria because they wanted brotherhood, they felt excluded. They were just unhappy. They didn’t know where they were going here.”

The story of Amer and the others might also identify a deeper issue. Brighton is often seen as a liberal city, but representatives from its Muslim communities claim that this is far from the truth. Mohammed Asaduzzaman runs a market stall near where the Deghayes boys once hung out, has lived in the city since 1966 and is a prominent figure among its Muslim population of 6,000. He accuses the city council of exploiting its black and ethnic minority community by using their support to attract funding. “They use and then forget us. We are not part of the decision-making process,” said Asaduzzaman. (A spokesman for the council denied this allegation. “This is absolutely not our approach and we are unclear as to what this claim is based on. All applications are treated on their individual merits.”)

A series of meetings were held last year to discuss integration in Brighton. According to internal notes, they found that many members of the city’s Muslim community felt “marginalised”, with disproportionately poor access to public services. The council does not employ a single full-time official to deal specifically with the needs of Brighton’s Muslim community.

In early February, I was able to contact Amer, who was stationed just over four miles from the frontline between Aleppo and Idlib. Despite the deaths of two brothers and his best friend, Amer said he felt content and liberated to have left behind the materialism and soullessness of a secular society. “I don’t think people realise they are being enslaved,” he said. There was no question, said the 21-year-old, that he felt more “belonging” on the Syrian battleground than he ever had in Brighton. “I feel like I’m doing something valuable and important compared to if I was in Brighton, living a normal life, having a normal job. I always used to ask myself what am I doing for the purpose of life.”

I feel like I’m doing something valuable and important compared to if I was in Brighton, living a normal life Amer Deghayes

Amer described himself as a member of the “mujahideen” instead of an al-Nusra fighter. “I offer my services for the whole of the Muslim nation. I’m not working with any particular group.” He insisted that he would never join Isis, however: “Their beheadings have caused harm to the mujahideen, the rebels. Their pictures should be showing the mercy of Islam.”

At the time of the interview, Islamist groups were embroiled in a vicious rearguard action to protect their territory in the north-west of Syria. Backed by Russian airstrikes, Assad’s forces were gaining ground. Amer confirmed his unit was getting “pushed from all directions” and, during one interview on 12 February, admitted he was anxious about the direction of the conflict.

A few weeks earlier, in January, his father had arrived in Idlib province, begging him to come back to Brighton. Amer told his father no, he will never return. “The moment my right foot left Britain it wasn’t home any more,” Amer said, although he admitted that he missed the seaside.

Then, the line crackling with interference as it faded in and out, Amer said he was hoping to die. “Of course, one of the main reasons I am doing this is so Allah gives me martyrdom and I get killed doing the most honourable thing in this life. You can call it selling your life for his religion, for his way of life.”

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