There are still those in France who cling to a view of the Belgians as a feckless, whimsical nation whose inbred stupidity makes them ideal fodder for any joke that involves mocking an imbecile. In that sense, the Gallic chauvinists' perception of their neighbours closely resembles English jingoists' attitude to the Irish. The resemblance between these two ancient prejudices has been heightened, of late, by the twisted perception that your typical Belgian, like his Irish counterpart - in addition to being idle, eccentric and hilariously dim - might also be capable, should the mood take him, of blowing you to smithereens. And that, as observers from all national backgrounds agree, is not very funny at all.

Belgium has produced more jihadi fighters, per capita, than any other western European nation and is estimated to have despatched around 520 recruits to the Islamic State cause in Syria. Even the idea of visiting the land that is home to the EU parliament is enough to inspire trepidation in some foreigners.

"Go to Brussels?" Donald Trump remarked on Fox News in January 2016. "I was there 20 years ago." Back then, Trump recalled, the Belgian capital was "so beautiful. Everything was beautiful." Now, he declared, "There is something going on and it's not good. They [the Belgians] want sharia law. There is something bad going on." Travelling to Brussels, Trump asserted, requires you to rub shoulders with people who are "living in a hellhole".

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The president didn't mention exactly what evidence had informed this judgement. The likelihood is that he'd been reading reports from the now world-famous quarter of Molenbeek-Saint-Jean in the centre of Brussels. Less than 20 minutes' walk from tourist attractions such as the Grand Place, Molenbeek covers 6 sq km and is home to about 95,000 people. All nine known perpetrators of the November 2015 Paris attacks had a connection with the neighbourhood. The March 2016 bombings at Brussels airport and the city's Maelbeek Metro station were planned there and executed by associates of Salah Abdeslam, who grew up in Molenbeek and has been described as a central architect of the Bataclan operations. The guns used in the Charlie Hebdo attack were sourced from the area. Two aspirant jihadis killed by Belgian police at Verviers, in January 2015, came from Molenbeek. In August 2015, Ayoub El Khazzani set out from there on his failed attempt to murder passengers on the Amsterdam to Paris high-speed train. The list goes on. As Charles Michel, the Belgian prime minister, put it, "Almost every time there is a terrorist attack, there is a link with Molenbeek."

Wander into a café in Molenbeek and introduce yourself as a reporter investigating the area's association with terrorism, and you'll be met with the kind of welcome extended to a foreign traveller in the first reel of a Dracula film, when he enters the village inn requesting a ride up to the castle.

"It's about time," one patron in the "Friends Of Molenbeek" café told me, "that the world had the decency to leave us in peace."

Molenbeek is the second poorest municipality in Belgium. Of its population, 80 per cent are Islamic, most with origins in north Africa, especially Morocco. Just under a third are unemployed. Few read the foreign press. But the global stigmatisation of their neighbourhood has not escaped anyone's notice.

"Instead of bombing Raqqa," the journalist Eric Zemmour observed recently, "France should be bombing Molenbeek." This is a place, another French journalist has claimed, "where you get beaten up for €5".

The Daily Express has described the area as "a conveyor belt of terrorism where Isis are heroes" and as a "seething city of Jihad".

In late 2015, the Daily Mail dispatched a reporter to this "crucible of terror". So grave are the perils awaiting any outsider mad enough to set foot in Molenbeek, their journalist asserted, that "my cab driver thought long and hard before agreeing to take me there". Upon arriving, the writer declared, "You feel as if you have entered some seething north African ghetto".

Read enough of this sort of thing and even the place names on the map start to look intimidating. It doesn't help that one of Molenbeek's main Metro stops, Etangs Noirs [Black Lakes] sounds like the gateway to one of the less hospitable areas of Mordor. Emerging from the station alone, as night was falling, it occurred to me that, given what I'd read about the frequency of assaults here, I could probably undertake a walk for charity sponsored not by the mile but the minute.

Nobody with their senses would seek to deny that Molenbeek has developed a unique connection with individuals capable of the most appalling acts. But the popular notion that the area is a more brutal version of south-central LA is nothing short of vaudeville. In the weeks I spent here I walked everywhere, at all hours. I confess to having occasionally dawdled on streets with a reputation for petty crime, close to the Brussels-Charleroi Canal, effectively inviting trouble. While it's not an exercise I'd necessarily recommend, the worst that happened to me was that a woman stopped to offer directions.

Brahim and Salah Abdeslam © Rex / Shutterstock

My HQ in the time I spent here was a beautiful old brasserie called La Saint Charles on Molenbeek's main artery, the Chaussée De Gand, handily placed between the Mr Cod fish-and-chip shop and one of Brussels' best restaurants, Les Trappistes. You can look out as long as you like from a window table in this family-run establishment without seeing anything that resembles what the British tabloids like to call "seething". That said, you are a block away from the site of Les Béguines, the former bar owned by brothers Brahim and Salah Abdeslam. Brahim blew himself up outside a restaurant during the November 2015 Paris attacks. Salah, his alleged accomplice in that slaughter, returned to Belgium and managed to hide out for 126 days before he was apprehended at a flat across the square from the mayor's office in Molenbeek.

Les Béguines © Rex / Shutterstock

Taki in the Spectator has described the district as a "no-go area" which police are too frightened to enter. The only time I was stopped against my will was in the main square, after midnight, when two plain-clothes policemen wanted to know why I was there. Molenbeek, I told them, didn't appear to be the vortex of undiluted evil that I'd been led to expect.

"Unfortunately not," one of the officers said.

Why unfortunately?

"Because if it was that simple," he said, "it would be easy to fix."

Safe house in Molenbeek © Getty Images

Most of the narrow streets are lined with attractive brick houses, many with wrought-iron balconies. As a non-Muslim you are in the minority and in some roads you do feel as if you're in Tangier: an experience you may or may not find exhilarating. The real question about Molenbeek is this: can it be described as a neighbourhood which is beyond the state's control, in the grip of sharia law, and a place where most residents are conniving to export death to the rest of Europe? And, if not, how is it that the neighbourhood has come to symbolise the terrorist threat against Europe in general and Belgium in particular?

For a dispassionate view, I went to Nigel Farage, who has famously struggled to embrace the pleasure of sharing public space with foreigners, and who, as an MEP, spends a great deal of time in the Belgian capital.

"Brussels," Farage told me, "is becoming increasingly lawless. It all begins with litter and with an unkempt look. Many crimes are now simply not reported. The last time I was mugged here, for instance, I simply didn't bother to inform the police. In large part, this is a failed city. I am very pessimistic," he added, "for the future of Brussels as a civilised place to live."

It's an irony not lost on its critics that the EU parliament - an organisation which seeks to radiate such qualities as efficiency, cohesion and fraternity - should be located in the heart of a nation whose divided political elite has bungled so many areas of governance that the Belgian state is widely regarded, and not just by Eurosceptics, as the basket case of Europe.

Brussels, wrote the historian Tony Judt, is "a metaphor for all that can go wrong in a modern city". The dysfunctional, chaotic and frankly shady nature of political life here has entered the realm of legend.

The capital has eight separate parliaments and 19 municipalities, each with its own mayor. Between the Flemish citizens and the French-speaking Walloons there exists a mistrust that neither side troubles to conceal. Brussels, technically the capital of the Flemish region, is dominated by Walloons. In matters of policing, where good faith and collaboration are crucial, this tribal acrimony has proved catastrophic. The city's 19 independent municipal police agencies were reduced to six following the last arrest of the paedophile and murderer Marc Dutroux, jailed for life in 2004.

Before Belgium acquired its reputation as a breeding ground for terrorism, the events surrounding Dutroux's crimes had been its greatest source of global scandal.

In 1989, the married electrician, then 33, was sentenced to 13-and-a-half years for the kidnap and rape of five children. Freed after three years, he was awarded a generous pension to compensate for the "psychological damage" he had endured in prison.

Melchior Wathelet, the justice minister who sanctioned his early release, was himself later accused, by two witnesses, of belonging to a child abuse network. The allegations were rejected after an investigation. Wathelet currently serves as advocate-general at the European Court Of Justice.

In 1995, Julie Lejeune and Melissa Russo, two eight-year-olds abducted and repeatedly raped by Dutroux, died in a dungeon beneath his house while he was serving a four-month term for car theft. In his absence, Michelle Martin, his wife and accomplice, fed dogs that guarded the cell but left the children to starve to death. Detectives ignored numerous tip-offs, one from Dutroux's mother. Police who visited his house heard, but failed to investigate, the sound of young girls screaming. Dutroux's wife was released in August 2012 after serving 16 years of a 30-year term.

Jean-Marc Connerotte, the judge at Dutroux's final trial in 2004, broke down in court while speaking about the bulletproof vehicles and armed guards deemed necessary to save him from assassination. Connerotte was removed from the case as a punishment for attending a fundraising dinner in aid of victims' relatives. Three-hundred thousand people marched in protest. The courthouse in the killer's home town of Charleroi was scrubbed down by locals armed with brushes and soap. You will struggle to find a Belgian who doubts that Dutroux was protected at the highest level. Reforms in the wake of the scandal have failed to restore faith in the police or judiciary.

What's Belgium famous for?" asks Colin Farrell's character in Martin McDonagh's classic 2008 film In Bruges. "Chocolates and child abuse. And they only made the chocolate to get to the kids." But of all the things Belgians are traditionally perceived to have been very bad at - these include sobriety, homicide investigations, driving, gun control, child protection and not hating each another - no area of failure has been quite so dramatic as their historical relationship with Africa. Britain, France and Spain may not always have distinguished themselves in their colonial adventures, but none of those countries' leaders managed to behave badly enough to have been accused, as has Belgium's King Leopold II, scourge of the Congo, of having outperformed Hitler in the matter of genocide.

It's not hard, if you are familiar with Leopold's modus operandi of rape, torture, executions and mass starvation, to imagine the leader of an African tribe calling to a lookout who is scanning the horizon in an attempt to identify the nationality of the Western settlers who are about to invade.

"Is it the Germans?"

"No."

"The Italians?"

"No."

"The Portuguese?"

"No. Oh. Dear God. It's... the Belgians."

If the casual barbarism inflicted on the Congo is a source of residual shame, Belgium's subsequent handling of immigration from north Africa has been hardly more distinguished. Certain streets adjoining Brussels' Gare Du Nord (in Saint-Josse-Ten-Noode, the poorest commune in Belgium, close to Molenbeek-Saint-Jean but not part of it) exhibit a flagrant lawlessness that would alarm anybody. It's here that Mehdi, a friend of a friend, takes me to meet some of his neighbours from Molenbeek. He leads me into a bar where every vice known to humanity is catered for. The only women present are Congolese and of a matronly build.

"Who are they?" I ask Mehdi.

"The maquerelles [female pimps]," he says. "They control the girls."

(Younger black women are displayed in windows along the street.)

"Who controls the pimps?"

"Who do you think? The police."

Mehdi, who boasts that this establishment is patronised by the father of a well-known Premier League player, is joined by two friends, Karim and Mohamed. All are in their late-twenties; all grew up in Molenbeek; and all are unemployed.

They embark on a litany of complaints of a kind that I would hear many times: considered unsuitable as job applicants once potential employers see the 1080 postcode on their CV, they feel trapped between, on the one side, racist thugs who threaten them on a regular basis and a far smaller number of IS sympathisers who look down on them for indifference to the cause. The white gangs, Mohamed says, are the bigger problem.

"We get attacked," he says, "and regularly insulted."

"In what terms?"

"Things like, 'F*** off back home you Arab scum,' he replies. "I was on the Metro last week and this group of them got on and pointed at my sports bag. They put their fingers in their ears and said, 'Watch him. It's ticking. We're all going up.' I managed to get off at the next stop. They stayed on the train, laughing."

Karim's late father, who came here 50 years ago, was a lathe operator.

"He lost his job," his son tells me. "Not long before he died he told me he wished he'd stayed in the Rif [northern Morocco]." As a boy, Karim says, one teacher laughed in his face when he said he would like to be a doctor. His immediate ambition is to become a hairdresser.

All three were brought up in the Islamic faith. Alcohol is not a temptation they seek to resist.

Do they get any help from the police?

"Listen," says Mehdi, "we [in Molenbeek] exist in a parallel universe. A different economy."

I tell him the area seems less threatening than I had expected.

"Things in Molenbeek," he says, "are opaque. People do get robbed and people do get radicalised. Some people see this as a form of warfare."

"So am I on the other side? Would I have had problems if I'd wandered into this bar on my own?"

"Probably," Mehdi replies. "Although you could be north African, just about. Maybe half. But you could also be a fascist. Or a cop."

"Maybe half", says Mohamed.

The other thing Mehdi adds is that, in Molenbeek, "Everybody knows everybody."

So did any of them know Salah Abdeslam, the former local currently awaiting trial in France on terrorist charges?

"No," Mehdi replies, without bothering to consult his friends.

Historically, Belgian jihadists have been more interested in IS than in religion. (Les Beguines, the cafe owned by the Abdeslam brothers, was closed on account of drug dealing.) Here, by the Gare Du Nord, as the evening wears on, the conversation is increasingly dominated by an anger fuelled by international politics.

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I mention that I knew Jacques Vergès, the late French lawyer who continues to be extremely popular with the north African community. One of the attorney's many notorious clients, the Venezuelan fighter Carlos The Jackal, described the lawyer as "a bigger terrorist than me". I saw Vergès a week before he died, when the lawyer told me, "I always remember the words of St Just [who helped draft the 1793 French constitution]. He said that terrorism was a legitimate political weapon: the last resort of the poor. Were the French Resistance," he'd asked me, "freedom fighters, or terrorists?"

"Have you seen the film of Aleppo?" Karim says.

"Yes."

"What do you feel? Guilt?"

"More horror. And helplessness. You?"

"Rage. Those are our brothers."

Could he go to Syria?

"Me?" He laughs. "Not personally."

"Are you saying you've known people who have gone?"

"Of course."

"Have they come back?"

A long pause.

"No."

They usually don't.

In the opulent lounge of the Metropole, one of Brussels' grandest old hotels, I meet Olivier. A white, French-speaking decorator aged 47, he was raised as a Catholic and is now a Buddhist. His son Sean, who grew up in Molenbeek, died in Syria in March 2013.

When did Olivier realise where his son had gone?

"He left with four friends," he replies, "in October 2012. They didn't warn anybody. Two weeks later I got a call. 'Hello, Dad. I'm in Turkey. I'm doing humanitarian work.' 'When will you be back?' 'I can't say.' I was already sick with worry. Then he called again. And this time, in the background, I could hear the sound of..." Olivier pauses, "tanks."

He has helped found a support group for parents who have lost children recruited to IS.

"I keep thinking, if I could go back in time, what could I do differently?" he says. "I feel I sensed the danger and did nothing."

Olivier is separated from Sean's mother, who is half Moroccan. His son was not raised as a Muslim.

"Sean was an ordinary kid," Olivier says. "He liked films, dancing, listening to music. All that stopped. He became withdrawn. He'd met this group who were giving food to the homeless. He thought he was doing good. Six months later he was on the front line facing the troops of Bashar Al Assad. He didn't last long out there."

"So these people exploited his better nature?"

"That's what makes it so sad. Sean had only been a Muslim for three years. He could have fallen in with good people. He didn't. But Islam - true Islam - has nothing to do with any of this."

"I assume you don't have Sean's body?"

"No. There's always part of me that believes one day I'll open the door and he'll be back. But two witnesses told me he died. One was his best friend, Sami, who went with him. We've had no news of Sami for two years."

"Who recruited Sean?"

"Older men who were very charismatic. Their propaganda was powerful. It sounds crazy but listening to him talk there were even moments when I started to wonder if he might be right."

"Where are these men now?"

"In prison."

© Getty Images

In Buffet Froid, the 1979 film by Bertrand Blier, one of the leading characters is Inspector Morvandieu, a homicidal detective who is asked, at one point, how many criminals he tries to convict. "As few as possible," Morvandieu replies. "Because in prison, they corrupt the innocent." As dark a line as that may be, I suggest to Olivier, you hear many stories about people who were recruited in jail, notably the El Bakraoui brothers, who orchestrated the Brussels attacks in March 2016. Both were radicalised in prison.

"It happens," says Olivier. "In the association we're working with the authorities to try to stop it."

"How?"

"We go into jails. We talk. We listen. We make contacts. We don't have a grand plan. All you can do is to try. I don't want," he tells me, "to see another one die."

I tell Olivier that I can comprehend, if not empathise with, a young man who grows up in Syria and decides to fight, on either side. But why here in Brussels? Why Molenbeek? Areas of Paris with a high Islamic population, such as the forbidding, soulless enclave of La Courneuve, are considerably more threatening to an outsider. Many parts of Molenbeek-Saint-Jean have an attractive, village-like atmosphere.

It's precisely this sense of community, Olivier says, that makes Molenbeek so difficult to penetrate. One phrase you often hear - "Everybody knows somebody who knows somebody" - hardly encourages residents to communicate suspicions to the police. "Things are more... occult here. There has always been something odd and secretive about the place. It has a peculiar energy."

Fear also fuels this collective omerta. I spoke to a former schoolteacher who, like many in Molenbeek, was unwilling for me to use her name. She described an attack that followed her speaking out against a group of young students.

Parents here who fear their children are being radicalised "just don't inform the police", says Montasser Alde'emeh, a researcher of Islamist extremism who runs a centre to discourage young men from travelling to Syria. "They have no faith in them."

One mother who did alert the authorities was Geraldine, a 50-year-old financier, and a colleague of Olivier's in the parents' organisation. She learned of the death of her son Anis via a text from an "IS commander". "Congratulations," it read. "He is now a martyr. Be happy he died fighting the unbelievers." Geraldine had known of Anis' plans to leave and informed the police. A week later he was in Syria. Magistrates had ruled it would be wrong to detain him as he was an adult.

It's the sort of decision that surprises nobody here. Two decades after the Dutroux scandal, the public still perceive the forces of law to have more in common with Clouseau than Poirot. Johan De Becker, head of the Brussels West Police region that includes Molenbeek, was reappointed five years ago, despite having received a conviction for involuntary manslaughter. De Becker (who was acquitted on appeal) had returned a firearm that had been surrendered by a policeman suffering from depression. The officer then used it to murder a woman.

The Abdeslam brothers lived and dealt drugs on a street adjacent to De Becker's office. When Salah Abdeslam was eventually arrested in Molenbeek on 21 March 2016, after police noticed an unusually large consignment of pizzas being delivered to his house, Belgian interior minister Jan Jambon warned of the likelihood of an imminent revenge attack. The bombings at Brussels airport and in the Metro took place the following day.

The aftermath of the attack on Brussels airport © Getty Images

In the fourth week of November 2015, when Brussels was in lockdown following the Bataclan attacks and with Salah Abdeslam still at large, a platoon of 20 soldiers was garrisoned temporarily at a police station in Ganshoren, north of Molenbeek, in De Becker's Brussels West area. On heightened alert, at one of the tensest periods in their nation's history, two policewomen, according to a December 2015 report in the newspaper La Dernière Heure, snapped into action and relocated to the soldiers' upstairs dormitory, where they had sex with eight of the new arrivals in what has been described as a "drink-fuelled orgy".

A police spokeswoman declined to comment on reports that the policewomen became "hot and crazy" when the soldiers arrived, stating that, "I cannot give more information. Investigations into the Brussels police are complicated. I don't want to trigger an internal fight."

The force has since denied the episode took place, saying that, "Measures have been taken" to discipline "the individuals responsible for these rumours."

Armed soldiers in combat fatigues are a common sight in Brussels hotel lobbies, on street corners and on public transport, but their presence doesn't necessarily inspire confidence. It's not uncommon to pass groups of privates lounging and gossiping, machine guns dangling by their sides. During the 2015 lockdown, a soldier carrying an automatic weapon was photographed clutching a shopping bag while on duty in the city centre. Morale is not what it could be. In January, 25 of De Becker's officers simultaneously applied for medical leave on the grounds that they were too fatigued to patrol.

Several of the military I spoke to on the streets of Brussels (theoretically a bilingual city) appeared not to understand French. Linguistic challenges are even more complex in Molenbeek, where many residents still speak only Berber, in which few surveillance officers are proficient.

Francoise Schepmans © Getty Images

Historically, politicians, rather than focussing on a cross-party assault on terrorism, have tended to turn on each other. Some blame Molenbeek's current mayor, centre-right politician Françoise Schepmans, in office since 2012, on whose watch the worst atrocities have occurred. Weeks before the Paris massacres, Schepmans was given the names of more than 80 terror suspects in Molenbeek. She took no action. "What was I supposed to do?" she remarked. "It's not my job to track potential terrorists."

Conservatives prefer to attack Schepmans' socialist predecessor, Philippe Moureaux, alleging that he was slow to react to growing radicalism. Moureaux, a distinguished academic and writer, met me in his apartment in the heart of Molenbeek.

How is it, I ask, that angry and disillusioned young men like the characters I'd met near the Gare Du Nord, seem inexorably drawn to Molenbeek?

"Brussels," says Moureaux (mayor for 18 years before Schepmans arrived) "is a segregated city. You have working-class areas in the north and the west, of which Molenbeek is one. In the south you have an affluent middle class, including many French civil servants, who move there because they pay less tax. There are two worlds. And there's almost no contact between them. For those kids you met, going to the wealthy side of the city is like visiting another planet. And vice versa."

For generations, he says, "Molenbeek has been the destination of last resort. First it was Flemish labourers employed in breweries along the canal. After the Second World War, Italians came to work in the factories. People called it Little Manchester."

The first great wave of Islamic immigration came in 1964, when Belgium signed agreements with Turkey and Morocco to bring in more industrial workers. Brussels' already close relationship with Saudi Arabia was reinforced in May 1967, after a fire destroyed a department store leaving 323 dead. By coincidence, King Faisal arrived in Belgium on a state visit a few days later. The Saudis poured money into the city in the wake of the catastrophe. The authorities handed Faisal the keys to the Great Mosque, the oldest in Brussels.

It was a gesture that helped cement the city's connection with Salafism, the ultra-conservative branch of Sunni Islam, closely allied to the Wahhabism, well-known for its determined attachment to sharia law.

"The fact that the people who arrived from Morocco in the Sixties came mainly from the mountains in the north and spoke Berber," says Sarah Turine, the young and highly regarded youth co-ordinator for Mayor Schepmans, "already fostered a notion of 'them' and 'us' which persists here. Each side demonised the other." The prevalence of Wahhabism, she adds, "has undeniably been a problem. This idea that we live among infidels and don't mix with them. For some in Molenbeek," she explains, "Syria was the last straw. That conflict has huge resonance here."

"Through social media?"

"Not so much. You read a lot of nonsense about sites like Sharia4Belgium [a now-defunct and always incompetent organisation based in Antwerp]. In Molenbeek, radicalisation has been conducted by people known to the target."

So does the problem reside in Molenbeek's 22 mosques? The day before I met Moureaux, newspapers were carrying reports of Mayor Schepmans having shut one down.

"What she closed was an unofficial meeting place," Moureaux told me. "It was a gesture. We never had any evidence that the trouble emanates from the mosques." Geraldine, mother of Anis, said that her son never attended mosques but was radicalised by people "on the street". Her opinion was echoed by almost everybody I met in Molenbeek. "The people that do this," one source told me, "are more familiar with a bar stool than a prayer mat."

It is ten years since the journalist Hind Fraihi wrote her outstanding book Undercover In Little Morocco. Fraihi was one of the first to describe what she terms Molenbeek's "synergy between crime and Jihad" and has come to be called "Gangster Islam", practised by small, secretive gangs who drew inspiration from marginal figures, such as Khalid Zerkani. Zerkani, a major organiser of radicalisation in Brussels, was imprisoned for 12 years in July 2015. The case for the defence wasn't helped by the fact that Zerkani's laptop contained tracts with titles including: "Thirty-Eight Ways To Engage In Jihad" and "Sixteen Must-Have Items If You're Heading For Syria".

At Zerkani's trial, witnesses testified that he had taught small street gangs that "stealing from infidels is permitted by Allah".

Anecdotal accounts concerning such groups aren't hard to obtain, although, as ever in Molenbeek, people are understandably reluctant to speak on the record. One source told me that he knew of bounties of as little as €300 being paid for the enlistment of naive recruits like Olivier's son Sean. The networks responsible, he claimed, are dominated by a Tunisian mafia. (Zerkani has close links with activists in that country.) The funds, my source insisted, originate from what he would only describe as "a very wealthy gulf state".

Such organised gangs, Philippe Moureaux acknowledges, do exist. Could he have done more to prosecute them?

"When I was mayor," he says, "we recognised the beginnings of fundamentalism. What we didn't have were these organised networks."

The key strategies required to combat terrorism are hardly difficult to identify. They include acute vigilance in local policing, adequate resources to infiltrate suspected terrorist cells and control illicit arms dealing, together with efficient frontier controls and swift cross-border exchanges on intelligence. On every level, Brussels is conspicuously under-served.

Belgium's internal problems are exacerbated by the Schengen Agreement, which permits free travel between 28 countries, and the nation's long-established reputation as the market of choice for illegal munitions.

"Until 2006," explains the Flemish Peace Institute's Nils Duquet, a leading expert on the trade in illicit arms, "you could walk into a store in Brussels and buy a gun without a permit. After that, you were supposed to obtain a retrospective licence for a weapon you owned. Many people never bothered. As a result, about 100,000 firearms went missing. They're out there somewhere, but they're not registered."

Terrorists, Duquet told me, have an understandable fondness for the machine gun. "Many dealers from the Balkans come here," he told me. "A Kalashnikov costs around €250 in Bosnia. In Brussels you can sell one for €1,500. What we see are numerous small consignments of these weapons smuggled in private vehicles."

He made it sound alarmingly easy.

"If you're a terrorist and you want to attack Paris, it makes perfect sense to organise it here in Belgium. It's a two-hour drive. Within the Schengen zone there are effectively no border controls. Where there are checks, there is a serious lack of co-operation across frontiers. There is no effective European police force. Europol is restricted to supporting co-operation between national police agencies."

So might it be overly simplistic, I asked Duquet, to suggest that all this killing is the fault of some evil at the heart of Molenbeek?

"Definitely," Duquet tells me. "Molenbeek has a certain reputation, in common with many other districts. Is it so different from other areas of big cities in Europe? I don't believe so."

A word you often hear in French language assessments of Belgian intelligence is "bavure", a noun which roughly translates as "cock-up". The bungled opportunities to arrest the guilty have been so glaring and numerous that they would challenge the credulity of a reader of pulp fiction: in particular the multiple failures to arrest Salah Abdeslam in his four months at liberty after the Paris atrocities. The vehicle carrying Abdeslam back to Brussels was stopped by French police at Cambrai, an hour's drive from the border. According to Jan Jambon, the Belgian interior minister, a database at the checkpoint began to blink red on Abdeslam 15 minutes after he had left the checkpoint.

Last year, the television station RTL produced an extraordinary documentary in which undercover reporters tested Belgian security at a variety of locations. They gained admission to Brussels' Palais De Justice carrying a detonator and 600g of a substance expertly engineered to resemble plastic explosive. Two journalists joined a tour party at the European parliament and passed through metal detectors carrying an imitation bomb and detonator, the apparent authenticity of which was approved by independent munitions experts. MEPs were sitting. The two managed to slip away from the tour guide, assemble and prime the device in the toilets, then rejoin the party without their absence being noted. Had the explosive been real, it could have been detonated in ten seconds.

Where the abilities of the Belgian national intelligence services are concerned, senior British politicians including former foreign secretary Lord Hague told me it would be inappropriate for them to comment. It's no secret, however, that the Belgian counterterrorism service has long been woefully under-resourced: a problem Prime Minister Charles Michel insists Brussels is addressing with some urgency.

"When it comes to exchanges of sensitive information," one retired British intelligence officer told me, "no national security agency is ever eager to initiate full disclosure with another. Of the European intelligence services one does have trust in, it is reasonable to say that Belgium is not in pole position. At the same time," he added, "I have some sympathy with the Belgians. Paris in particular is always looking to blame Brussels for mistakes the French have actually made themselves." Combatting terrorism by intelligence alone, he added, "is a quite impossible task. If the Belgians have somebody 'on the radar' and the suspect manages to commit a terrorist act, it's their fault for losing track of them. If they haven't identified them as a threat, it's their fault for having missed them."

The current level of threat facing Europe, according to Claude Moniquet, a former French intelligence officer and director of the Brussels-based European Strategic Intelligence And Security Center, is "different to anything we've ever experienced before. We could be talking about 8,000 to 10,000 potential suspects." A truly foolproof surveillance operation, observing a single suspect for long periods, Moniquet says, requires 30 to 40 operatives.

Just as worrying as the way the Belgians have dealt with the guilty, is their handling of allegations against the innocent. Following the 22 March 2016 bombings in Brussels, Human Rights Watch detailed 26 incidents of alleged misconduct by the Belgian police, mainly involving use of excessive force.

Ibrahim and Khalid El Bakraoul © Rex / Shutterstock

During an interrogation of the taxi driver who drove the three terrorists to the airport, the Brussels constabulary showed the man the now famous photograph of three figures: Ibrahim El Bakraoui and Najim Laachraoui, terrorists who died at the scene, accompanied by the third, mysterious, "man in the hat" who walked away from the slaughter. Detectives became convinced that the survivor was Fayçal Cheffou, a freelance journalist and political activist based in Brussels.

On the afternoon of 24 March, Cheffou told me, he was travelling by car across the capital.

"I was alone in the back seat," he said. "A friend and his sister were in the front. Suddenly this blue Ford cut across us and blocked the road. Other cars hemmed us in from the sides. Men in plain clothes appeared, carrying automatic weapons. So I'm sitting in the back. To my left I have one guy yelling, 'Open the door!' To my right, another one's shouting, 'Don't move, or I'll shoot!'"

"Did you know why they'd stopped you?"

"I had no idea. I didn't move a muscle. I was worried because I could see their hands were shaking. I remember thinking: if I move, they're going to do something stupid here. They got me out, put me on the ground then drove me to their headquarters." There, Cheffou says, "they gave me a full body search. They wanted fingerprints, a DNA sample, and to swab me for explosives. I asked why. They wouldn't reply. I said, 'I want to see my lawyer.' They said, 'Your lawyer is dead.'"

Cheffou, known to the police for less serious offences, bears scant resemblance to Mohamed Abrini, the Belgian national who, after his arrest on 8 April 2016, admitted in a police interview that he was the man in the photograph. Cheffou was cleared after phone records confirmed he was at home at the time of the atrocities. During the five days he was held, he claims, he was beaten to the point of unconsciousness.

When his lawyer finally arrived, he says, "he pointed out that the man in the hat not only looked nothing like me, but his hands, in that famous picture, are all over the airport trolley. Meaning it was covered in his fingerprints. They did nothing to investigate that for three days."

Cheffou has alleged more serious abuse at the hands of police, which will constitute the basis of an appeal for compensation once the inquiry has been formally closed.

What had been the consequences of the experience?

"For five days," he says, "I was the most hated man in Belgium, if not the world. Even now, people point at me on the street. My life has been ruined. You should try applying for a job when if they google your name, all that comes up are pictures of police and body parts. All I can say is that after something like this happens to you, you will never be the same."

"It sounds like something out of Hitchcock."

"It was."

"When will the police investigation be over?"

"Nothing would surprise me of them. I was summoned to the police station not long ago. The questions they asked me were just surreal. Was I left-handed? What was my opinion of the press? What did I think of the bombings in Turkey? It's glaringly obvious," Cheffou adds, "that I am not the man in the picture. Those were the five worst days of my life."

© PA Photos

With the exception of one or two individuals concerned with enforcing or evading the law, I met nobody, in my time in Molenbeek, who was not striving to do their best for the district. That includes community leaders, schoolteachers, deradicalisers, doctors, the current mayor's office, Philippe Moureaux and a Belgian intelligence officer who described the challenge of combatting extremism here as "like trying to arm-wrestle tear gas". Anti-terrorism, he told me, is "a discipline in which progress is far harder to identify than failure". The chances of another atrocity committed by people with links to the area, everyone agreed, seem highly likely.

"What you have here in Molenbeek," said Olivier, father of Sean, "is an entire generation of young men who are sleepwalking through despair. They're living in what people tell them is the heart of Europe and yet they feel utterly excluded, which makes them very easy to manipulate. But what I would like to say, loud and clear," Olivier added, "is that this tragedy does not simply have to do with Molenbeek-Saint-Jean, or even just with Belgium. This is not some local difficulty. It is a global catastrophe. The thing about evil is that it very quickly gets you noticed. What is so terribly sad, where Molenbeek is concerned," Olivier said, "is that outsiders tend not to see that there are good people here too."

Originally published in the April 2017 issue of British GQ