PARIS - The Paris terrorist attacks were carried out with the help of three French brothers living in Belgium, the authorities said on Sunday, as they asked the public's help in finding one of them.
The French authorities said they were seeking Salah Abdeslam, 26, and described him as dangerous. The police warned the public: "Do not intervene on your own, under any circumstances."
Belgian officials said that one of his brothers had died in the three-hour massacre, which killed at least 129 people; another brother is in detention in Belgium.
Officials had initially described eight attackers, but on Saturday night said that only seven attackers had died - six by blowing themselves up and one in a shoot-out with police.
The carefully coordinated attacks on Friday night, which President François Hollande of France says are the work of the Islamic State, increasingly appear to have involved extensive planning by a network of men with sophisticated weapons who plotted their attack from outside the country.
The French interior minister, Bernard Cazeneuve, after meeting in Paris with his Belgian counterpart, Jan Jambon, said the attackers had "prepared abroad and had mobilized a team of participants located on Belgian territory, and who may have benefited - the investigation will tell us more - from complicity in France."
Crucial, if sparse, details about four of the attackers came into view on Sunday.
One attacker - nationality not yet known - evidently posed as a Syrian migrant. The Serbian newspaper Blic published a photograph of a passport page that identified its holder as Ahmad al-Mohammad, 25, a native of Idlib, Syria. He passed through the Greek island of Leros on Oct 3 and the Serbian border town of Presevo on Oct 7, officials in those countries said. It was not clear whether the passport was authentic; the civil war that has sent millions of Syrians fleeing and fuelled the rise of the Islamic State has also created a large black market for forged Syrian passports.
Paris police are on full alert and tensions are high, as this routine traffic stop on Sunday showed.
At least three other attackers were French citizens. Two had been living in the Brussels area, including one in the community of Molenbeek, according to the Belgian authorities. The third was Ismael Omar Mostefai, 29, a native of Courcouronnes, France, who had been living in Chartres, 100km southwest of Paris, and who, along with two other gunmen, killed 89 people at the Bataclan concert hall.
Mostefai was the middle of five children born to an Algerian father and a Portuguese mother, and he once worked at a bakery, according to a former neighbour at the housing development just outside Chartres where the family used to live.
"It was a normal family, just like everybody else," said the neighbour, who spoke on the condition of anonymity. "He played with my children. He never spoke about religion. He was normal. He had a joie de vivre. He laughed a lot."
For reasons that are unclear, Mostefai changed. "It was in 2010, that's when he started to become radicalised," the neighbour said. "We don't understand what happened."
As the authorities continued to examine Mostefai's motivations and background, other clues emerged from official accounts in France and Belgium.
Two vehicles used in the attacks had been rented in Belgium early last week, the federal prosecutor for Brussels announced on Sunday. One of them, a grey Volkswagen Polo, was abandoned near the Bataclan after being used by the three terrorists who died there.
The other, a black Seat Leon, was found early Sunday morning in the eastern Paris suburb of Montreuil. Three Kalashnikov rifles were found inside it. The vehicle may have been used as a getaway car for the shooters at restaurants in central Paris.
The Belgian authorities also announced that they had detained seven men. Three of them passed through a roadside check in Cambrai, France, at 9:10am Saturday, while on the A2 highway heading to Belgium. They made their way to Molenbeek, where the authorities detained them for unknown reasons and seized the car on Saturday afternoon.
Fundamental questions remained: how the terrorists, who acted in three synchronized teams, managed to pull off the deadliest terrorist attack in Western Europe since 2004, and whether they received direction from Islamic State leaders in Iraq and Syria, who until now had never taken responsibility for such a large-scale attack in the West
The revelations that three of the attackers were French citizens were likely to exacerbate long-standing fears in France about the place of Muslim immigrants and converts in French society, 10 months after a smaller set of deadly attacks on the satirical newspaper Charlie Hebdo, on a kosher grocery and against a police officer.
Mostefai was identified in a Facebook post by the mayor of Chartres, Jean-Pierre Gorges. He was one of three hostage-takers at the Bataclan, and who was identified based on a print from his severed finger.
Mostefai was born in the town of Courcouronnes and grew up around Chartres, where he lived until 2012. According to the Paris prosecutor, François Molins, he was arrested in connection with a series of low-level crimes from 2004 to 2010 and had been under surveillance since 2010, having been flagged in a French security services database as someone who had fallen under the influence of extremist Islamist beliefs.
Six of his relatives have been detained for questioning; on Sunday, other relatives told French television that he had been estranged from them after a falling-out.
In his Facebook post, Gorges expressed despair and frustration.
"How many deaths will occur before our political leaders understand and take action?" he asked, describing the "emotion, incomprehension and anger" he felt at the deaths.
Gorges called for strong action, without asking questions first "Our leaders don't need to prove they are legitimate: We have elected them so they take responsibility of the executive power of the republic," he wrote on Facebook. "Their duty is to act effectively, and ultimately we don't need to know how."
On Sunday, Hollande met his predecessor and political rival, Nicolas Sarkozy, at the Elysee Palace. Afterward, Sarkozy urged decisive action against the Islamic State - a position Hollande has also taken.
"We need everybody in order to exterminate Daesh, and especially the Russians," Sarkozy told reporters, using an Arabic acronym for the Islamic State.
Russia's president, Vladimir Putin, is a steadfast ally of Syria's embattled president, Bashar Assad, and recently began an aerial bombing campaign in Syria. The United States and France say the attacks have not been aimed at the Islamic State, as Putin claims, but at other groups opposing Assad.
Sarkozy, who has been known to be tough on immigrants during his tenure as president, cautioned against linking the refugee crisis with the terrorist attacks, but added: "We need, together, to rein in the wave of migration ensuing from the Syrian situation."
As President Barack Obama and other leaders of the Group of 20 advanced and emerging economies gathered for a scheduled summit meeting in Antalya, Turkey, on the doorstep of the Syrian crisis, Hollande stayed behind in Paris, his nation in mourning.
As the investigation proceeded, Obama told reporters in Turkey that the "skies have been darkened by the horrific attacks" in Paris and pledged that America would support France, its oldest ally.
"We stand in solidarity with them in hunting down the perpetrators of this crime and bringing them to justice," Obama said after meeting with Turkey's president, Recep Tayyip Erdogan, at the start of a 10-day trip that will also take him to the Philippines and Malaysia.
At the same summit meeting, the president of the European Commission, Jean-Claude Juncker, said there was no need for a complete review of the bloc's refugee policy in response to the terrorist attacks.
"Those who organized, who perpetrated the attacks are the very same people who the refugees are fleeing and not the opposite," the AFP news agency quoted Juncker as saying. "And so there is no need for an overall review of the European policy on refugees."
Pope Francis on Sunday deplored the terrorist attacks in Paris, which he described as an inconceivable "barbarity" and an "unspeakable affront to human dignity" that "leaves us shocked" and must be condemned.
"The path of violence and hatred does not solve the problems of humanity, and using the name of God to justify this path is blasphemy," Francis told thousands of pilgrims gathered in St Peter's Square for his weekly Angelus address.
"We wonder how the human heart can conceive and carry out such horrific events, which have shaken not only France but the whole world," Francis said, before asking the faithful present to pray with him for the victims of the attacks.
Security measures at St Peter's, already significant, were increased on Sunday. The Italian government on Saturday said it would bolster surveillance of potential terrorist targets.