November 17, 2015 4:55 pm

Europe faces an unprecedented threat from Islamist terrorism. So much so that the head of the Direction Générale de la Sécurité Intérieure, France’s domestic intelligence service, warned only last month that not every jihadi plot could be stopped.

But given their scale and complexity, many are now asking whether the Paris attacks were indeed inevitable, or whether there were mis-steps along the way that Europe’s spies should have avoided.

French authorities have named Abdelhamid Abaaoud, a Belgian of Moroccan origin, as the potential “mastermind” behind the attacks. Mr Abaaoud, 27, fought with Isis in 2013 in Syria, where he took part in atrocities before returning to Belgium in 2014. He had been in contact with Mehdi Nemmouche, a Franco-Algerian jihadi who shot four people dead at the Brussels Jewish museum in May that year.

Mr Abaaoud, also known as Abu Omar al-Belgiki, fled Europe in January this year after police broke up a terror cell of which he was part in Verviers, eastern Belgium. After his escape he taunted European authorities in an interview in Dabiq, Isis’s glossy propaganda magazine. Intelligence officials later linked him to at least two other terror plots in France: the Villejuif church attack in April and the failed gun rampage on a Thalys high-speed train in August. He was also linked to an early-stage plan, uncovered by August, to perpetrate a massacre at a crowded music venue. Mr Abaaoud was a top priority signals intelligence target for the French — a high-value individual, or HVI, on the anti-Isis coalition kill list. So why were his communications with members of the Paris attack cell not intercepted? One senior intelligence official told the Financial Times Mr Abaaoud was a “skilled operator” and suggested the use of encrypted communications was key to the way he and the Paris plot evaded detection.

High-risk profiles

Five of the eight Paris suspects had fought for Isis in Syria. Questions will be asked about why they were not monitored closely given the known risks that such a profile entails. (Current academic research suggests at least one in five returnees will attempt an act of political violence.) Most of the plotters had long been known to intelligence agencies as figures in European Islamist circles. Suicide bomber Omar Ismael Mostefai, 29, had a French police “S file” indicating his status as a potentially dangerous radical since 2010. The sheer number of such peripheral figures that European counterterror officials must track is daunting, but the Paris plot required eight of them to be in regular communication and to have trained together. Even if their profiles did not trigger intensive surveillance individually, their regular association should have done. Many will ask about the gaps in the system that prevented that.

Rapid radicalisation

In the age of social media-led propagandising and the dynamic narrative Isis has woven about its jihadi credentials, intelligence services talk about fast-track radicalisation. And often the speed of the shift in an individual’s religious beliefs is an indication of its danger. At least two of those involved in the Paris plot changed their behaviour and lifestyle significantly in the months that preceded the attack. The Abdeslam brothers, Ibrahim and Salah, were drinkers and gamblers until a year ago, when they both suddenly stopped. Bilal Hadfi, the “baby-faced jihadi”, also turned to hardline political Islam in the last year. In July, he wrote on his public Facebook account, which is littered with pictures of automatic weapons: “Hit the pigs in their communities so they no longer feel safe even in their dreams.” He had already travelled and returned from Syria. His social media output alone should have flagged him to Belgian authorities.

Molenbeek warning signs

The Brussels district has become notorious as a hub of jihadism in the heart of Europe. It has been linked to four terror attacks that were not picked up by intelligence agencies in the past 18 months alone. Nemmouche, who took part in the Brussels shootings of May 2014, and Amedy Coulibaly, the third attacker in the Charlie Hebdo attacks in January, acquired their weapons in Molenbeek. Ayoub el-Khazzani, 26, the Moroccan-born Spaniard who came within a whisker of committing mass murder aboard a train in August this year, was a regular worshipper at an unofficial, radical mosque in the district. In light of those associations and of the countless other plots or connections the district has spawned, questions will be asked about monitoring. Jan Jambon, the Belgian home affairs minister, said this week that security authorities “do not have control of the situation in Molenbeek”. Such an admission should be enough to put intelligence agencies across Europe on edge. The Belgians insist they are doing all they can but many of their peers in other European counter-terrorism agencies wonder if it is anything like enough. Per capita, Belgium has a greater foreign fighter problem than any other country on the continent.

Turkey’s alert — Mostefai

According to Turkish government officials, Ankara warned France three times about the risks posed by the Bataclan bomber Mostefai, who was known to French authorities as a radical. In October 2014, the Turks said he was a “terror suspect” after linking him to Isis attack planning cells in Syria. In December last year they sent another warning about him to the French. In June this year they reiterated it. The French did not request additional details from the Turks until after the attack. Intelligence co-operation and sharing with Turkey remains one of the most problematical elements of the challenge for European countries battling Isis.

Iraq’s warning — a sleeper cell

The day before the attack in Paris, Iraqi intelligence officials alerted counterparts across the anti-Isis coalition, France among them, that Isis had ordered attacks in Europe. A sleeper cell was now active in France, the Iraqis said, directing an operation planned in Raqqa. Though with hindsight such information seems spot on, intelligence officials stress that it lacked enough specific information at the time to trigger a serious investigation. Warnings about Isis’s ambitions are frequently received, they noted, and difficult to act on in the absence of operational detail.

Border controls

The identity of the third Stade de France suicide bomber remains a mystery. A Syrian passport in the name of Ahmad al Mohammad that was found near his remains is almost certainly a fake. Most likely he was known to authorities as a foreign fighter with Isis in Syria and had used the false documentation to sneak back into France. Questions will inevitably be raised about how European authorities can enforce rigorous checks on passports from the Levant as a result. But there are more basic problems. Sami Amimour, the gunman at the Bataclan, was a wanted suspect in France. He had been under judicial supervision since 2012 after he tried to travel to Yemen to fight with al-Qaeda. An international arrest warrant was issued in 2013 after he absconded and went to fight for Isis in Syria. Somehow, however, Amimour returned to Paris — according to friends several weeks ago — without raising concerns among security officials.

The German arms cache

On November 5, a week before the attack, a 51-year-old Montenegrin man was stopped in his car in a routine check by police in Bavaria. His vehicle was laden with grenades, automatic weapons, dynamite and ammunition. His GPS was set for an address in Paris. Joachim Herrmann, Bavaria’s interior minister, said: “There are reasons to suspect that this is about terrorist intentions, or someone supplying weapons to terrorists.” German and French authorities are investigating a potential link to the Paris cell, but regardless of what they can establish, the discovery of such a large consignment and information about the likely destination should have been a cause for heightened concern.

Sourcing explosives

Making large quantities of explosives is not an easy task. It is yet to be determined exactly what the attackers used to manufacture the suicide belts they used at the Bataclan and Stade de France. However, it is likely that they contained TATP, a highly unstable peroxide-based explosive used in the second, abortive London Tube bombing attempt in 2005, or a nitrogen-based compound. Ever since the London and Madrid terror attacks, the sale of substances that have potential use in bomb making has been closely monitored. In some countries there are safeguards in place that stop sufficient quantities of key chemicals being sold at any one time, or that require shops to report purchases to security authorities. Where the attackers sourced their chemicals and why the sales were not flagged up will be a key question for authorities to answer.