CHARTRES, France - Ismael Omar Mostefai, the first of the perpetrators of the bloody massacre in Paris to have been identified, personified the dilemma facing French authorities as they struggle to fight an enemy they cannot find.
Tall with a slight beard, often clad in a djellaba robe, the 29-year-old French citizen lived in a modest house in a suburb of Chartres, a town southwest of Paris far better known for its magnificent cathedral than as a hotbed of Islamist radicalism. "He was a normal man," said his neighbour Christophe.
"Nothing made you think he would turn violent."
Asked about media reports that he had a wife and a young daughter, he said he always saw Mostefai alone.
Karim Benayed, an official at the local mosque, said Mostefai was not a frequent visitor. "I may have bumped into him but I didn't know him," he said.
"He may have passed through here but he didn't get radicalised here."
In the wake of the carnage on Friday evening that killed at least 129 people, French investigators have found out a lot more about Mostefai, who blew himself up after helping stage Friday's worst single massacre at the Bataclan rock music hall.
They also found worrying gaps in their intelligence.
It turns out that a police dossier had already marked him as a potential Islamist militant. He had eight convictions for petty crimes, but had never been in the prisons where authorities watch for signs of radicalisation.
Turkey says it notified French authorities twice about him, in December 2014 and June 2015, presumably on his way to or from Syria. Mostefai entered Turkey in 2013 but there was no record of him leaving. Paris only asked for more information on him after Friday's attacks, a senior Turkish official said.
"We did not connect the dots," criminologist Alain Bauer told Le Point magazine after the Paris killings. "We knew for several weeks that we were facing a major risk toward the end of November or early December." The French Interior Ministry had no immediate comment on the Turkish assertion.
Marc Trevidic, who until September was France's top magistrate for terrorism cases, revealed that authorities even knew the kind of targets Islamic State had in mind.
After 10 years on the job, he interviewed his last suspect in mid-August. "The guy admitted that he was asked to hit a rock concert," Trevidic told France 2 television.
"We didn't know if it would be Bataclan or another place, he didn't know the exact location that would be designated. But yes, that's what they asked him to do," he said with the exasperation of a man frustrated by a missed opportunity.
Dalil Boubakeur, rector of the Paris Grand Mosque, said Salafists - followers of the same radical puritan ideology as Islamic State - were infiltrating mosques in France and sending young people to Syria, especially converted Europeans.
"We've had provocateurs here spilling out hostility and violent diatribes against the state and those who don't want to follow their jihad," he told Reuters.
"We've urged authorities to be firm and asked police for help, without success."
France has reacted to the attacks by declaring a state of emergency and raiding homes of suspected militants around the country. Its fighter jets have hit two training camps and a suspect arms depot in and around the Islamic State's unofficial capital of Raqqa in Syria.
Foreseeing such strikes, defence analyst Francois Heisbourg said on Saturday: "We can bomb Raqqa to the ground, but it's not clear that would help us foil this type of attack in Europe.
"We don't just have a problem in Syria, we have a problem in France," he told iTele television.
Another surprise in the Paris attacks is the high level of coordination and use of suicide bombers, which goes against the prevailing view that Islamic State used mostly "lone wolves" who would fight to the death but not turn into walking bombs.
"This is what all the specialists feared because it's technically much harder to detect," said Arnaud Danjean, a European Parliament deputy and former intelligence officer.
"Until now, it was culturally not in the tradition of French activists," he said.
"Today, that taboo has fallen. There are French citizens ready to blow themselves up in France, among French people."
Since the United States' Sept. 11 attacks, France's struggle against homegrown jihadists has gone through several phases. It has infiltrated "hot mosques", expelled radical preachers, banned headscarves in state schools and created what turned out to be an ineffective national Muslim council.
Trevidic said these efforts missed the fact that many militants were radicalised not in mosques or in prisons, but over the Internet and through trips to Syria.
"For 10 years, we did nothing" to tackle the problem of individual radicalisation away from the more obvious militant groups, he said.
"We only started doing this two years ago."