How did France miss signs of terror to come?

GENNEVILLIERS, France — The Grand Mosque in Gennevilliers, a suburb just north of Paris, is a source of pride for many of the area's 25,000 Muslim residents. Years in the planning, it cost about 2.3 million euros (about $2.6 million) to build and opened nearly six years ago. Now about 2,500 people crowd into the mosaicked hall for Friday prayers under its soaring dome and huge crystal chandelier.

Until two weeks ago, one familiar face in the crowd was a devout 32-year-old man, a French-born Muslim of Algerian origin, who lived in a yellow-brick apartment building a few streets away. His name: Chérif Kouachi.

As French officials try to piece together how Chérif Kouachi, 32, and his brother Saïd Kouachi, 34, were able to mount the deadliest attack on civilians in modern French history — the Charlie Hebdo massacre, in which 12 people were killed — there is one question they have to answer: How did they miss warnings of the plot, despite knowing that Chérif Kouachi had been jailed for trying to fight U.S. troops in Iraq and that Saïd Kouachi had traveled to Yemen for weapons training from Al-Qaeda?

Three days of violent turmoil in Paris included the fatal shooting of a policewoman by Amedy Coulibaly, 32, who claimed allegiance to ISIL and killed four hostages in a kosher supermarket. It has since emerged that Coulibaly and Chérif Kouachi were involved in a plot to spring from jail the man who bombed the Paris Métro in 1995.           

For French officials, knowing how the intelligence failed is crucial for the country — and the rest of Europe — for one overriding reason: It could help stop the next attack.

The threat appears all too real. On Thursday Belgian anti-terrorism police stormed an apartment in the town of Verviers, killing two people who recently returned from fighting in Syria and who were allegedly plotting an attack in Belgium, according to prosecutors. French police said on Wednesday they were hunting for a missing fourth gunman from last week's attacks — Coulibaly's accomplice — who they believe shot a jogger in a park and then fled, possibly to Syria.

About 3,000 Westerners have joined armed rebel groups in Syria since 2011, about one-third of them French. Many Europeans are anxious about what could happen when battle-trained fighters start to filter home. "Of course it is impossible in all of Europe to monitor every guy coming from Syria or Iraq," said Yves Trotignon, a former French intelligence official who now runs Risk & Co., a terrorism consultancy in Paris. "We in the intelligence community know that it is impossible." 

Another way to gauge how difficult it will be to avert attacks is to catch the Métro up to Gennevilliers, where Chérif Kouachi had lived since 2012.

In the Grand Mosque’s office, the staff said that although they had seen him for years at Friday prayers, few had gotten to know him well. He ate alone and largely kept to himself. When police released the Kouachis’ photographs to television channels during the manhunt for the pair — having found Saïd Kouachi’s identity card in the getaway car — their faces sent a thunderbolt through the mosque's members. “It was a total shock because we had seen him in the mosque,” said Ali Heraz, 28, the mosque's administrative secretary. Aguida Derradji, 70, a board member of the mosque, said Chérif Kouachi attended Friday prayers most weeks but added, “I never spoke to him.”

Heraz said the mosque’s association organizes interfaith events as a way to “instill a sense of living together” with non-Muslim French. (France’s 5 million Muslims make up about 6.5 percent of the population.) But Heraz says the mosque has limited pull over its members; stronger influences lie elsewhere. “People are being radicalized by the Internet and also in prisons. In prison they have contact with these people,” he says, referring to extremists.

At the Sahara kebab restaurant a few doors down from Chérif Kouachi’s old apartment at 17 rue Basly, a resident who was released on Wednesday from a prison in Bois d’Arcy outside Paris said that he and other inmates watched the live coverage of the Charlie Hebdo attack and its aftermath in prison — and that many saw the attack on the magazine as justified. “To be honest, most people were happy about Charlie Hebdo. That is the truth,” said Soufian, who knew Chérif Kouachi and would not give his last name. Echoing other residents in Gennevilliers, Soufian said he believed global sympathy over the attack was overblown. “I see more people killed in Gaza, but when these journalists died, everyone marched for them,” he said.

Stanching all attack plots will take immense effort not only in France but across Europe and beyond.

France and the U.S. would like to increase Internet surveillance and travel restrictions on suspected radicals. Last summer French Interior Minister proposed six-month no-fly restrictions for such people and requirements that airlines tell the government when they try to reserve a ticket. And last Sunday, just before the giant march kicked off in Paris, interior and justice ministers from Europe, Canada and the U.S. (including Attorney General Eric Holder) holed up in a crisis meeting. In a joint statement afterward, they said that they wanted Internet service providers to help governments monitor suspected extremists and that they saw a “crucial and urgent” need for the EU’s 28 countries to share passenger information as a way of stopping potential attackers from traveling across the continent and to Syria.

All those are ideas that French civil-rights groups and many European politicians have bristled at in the past. It is not clear that such measures would have stopped the Kouachis, who were already on U.S. and British no-fly lists and had not returned from Syria.

Many who knew Chérif Kouachi in Gennevilliers say they missed signs that he was planning an attack and that he stashed weapons in his fifth-floor apartment in their quiet neighborhood. “You cannot know what goes on behind closed doors,” said Ahmed Ben Mohammed, 43, who works at the kebab restaurant, as he sliced meat for lunchtime customers. “Some people who look evil are nice and those who look nice are evil.”

Left to pick up the pieces, French officials and police are now pondering two possibilities: That there were serious holes in their work or that the task of stopping attacks is just enormously difficult. “Either intelligence services took their eyes off these people and they grabbed the opportunity,” said Trotignon, “or they were simply better.”