How many attackers are on the run? Seven of the terrorists who carried out a series of co-ordinated attacks in Paris on Friday night were killed: six blew themselves up by detonating explosive vests and the seventh was shot dead by police when they stormed the Bataclan concert venue.
But French police are certain that at least one and possibly more attackers are still at large. An international manhunt is continuing for French national Salah Abdeslam (26), who is believed to have been part of the group that shot dead more than 40 people at four cafés and restaurants in the 10th and 11th arrondissements.
A second suspected member of that group - Salah’s brother Brahim (31) - entered a cafe near the Place de la Nation at 9.40pm on Friday and, just as a waitress was about to take his order, detonated his explosive vest.
Salah escaped in a black Seat car, which was found abandoned with three Kalashnikovs in Montreuil, on the eastern edge of Paris, on Saturday.
The authorities have admitted that Salah was in a car that was stopped by police near the France-Belgium border on Saturday, but as his name was not at that time flagged in the security services' alert system, the car was waved through the checkpoint.
Investigators are increasingly certain that at least one other attacker is on the run.
A number of witness statements from survivors at the Carillon, Petit Cambodge, Belle Équipe and Casa Nostra - bars and restaurants targeted in the mass shootings – suggest there were three men in the black Seat the gunmen were travelling in. That would leave one unidentified man unaccounted for.
Were there accomplices? The investigation has already expanded beyond the attackers to the wider support structure that inspired, funded and facilitated them.
In addition to the two suspects on the run, police believe at least four other people helped organise the attacks. Attention is focusing on the Molenbeek suburb of Brussels, where the Abdeslam brothers lived.
Belgian police have arrested two men who travelled with Salah Abdeslam from Paris to Belgium on Saturday. According to French press reports, the men claim Salah asked them to give him a lift without telling them what he had been doing in Paris.
Then there's the Raqqa connection. The authorities believe the attacks may have been ordered by Abdelhamid Abaaoud, a Belgian national now living in Syria, where he has become an Internet propagandist for Islamic State under the nom de guerre Abu Omar al-Belgiki - the Belgian. Abaaoud, who is also from Molenbeek, is a friend of Salah Abdeslam; the two were imprisoned together in Belgium in 2010 for armed robbery. The Raqqa-based militant is believed to have been the "brain" of the cell in Verviers, Belgium, that was dismantled a few days after the Charlie Hebdo attacks last January. Abaaoud eluded arrest and returned to Syria, where the French military targeted him in an air raid last month. Why did the three Stade de France bombers blow themselves up at locations where there were so few people? The co-ordinated, near-simultaneous attacks on Paris were carried out by three teams: the first went straight to the Bataclan, the second targeted cafes and restaurants in the 10th and 11th arrondissements and the third comprised three suicide bombers who blew themselves up outside the Stade de France, north of the city. The stadium attack, which occurred during the first half of a France v Germany friendly match, is the most mysterious, and the one investigators know least about.
Accounts differ on whether the attackers had match tickets, and how much effort they made to gain entry. Did they plan to enter the stadium with the fans?
Did they think they could force their way in? And why, when they could not gain entry, did they detonate their explosive vests at locations where there were relatively few people? What was the Bataclan attackers’ plan? Two hours after the three assailants entered the Bataclan by calmly walking through the front door and opening fire, the police - who by now had surrounded the venue - made their way into the building and were preparing to storm the rooms where the attackers were holed up.
At that point, one of the terrorists shouted a phone number to the commandos, who passed it on to their specialist negotiator. The two sides never negotiated, however.
The police say they spoke to one of the attackers five times but that each time the gunman simply told the police to leave or else they would continue shooting.
The authorities believe the terrorists, who by that stage had killed scores of people, had no intention of talking. Did they have demands? Did they plan to take hostages? Did they hope to escape?
At 12.20am the head of the police ordered the elite unit to storm the room. After an exchange of heavy gunfire that lasted three minutes, all three attackers were dead.
Describing the bloody scene that greeted the police in the main hall, where hundreds of bodies lay sprawled on the floor - some of them dead, others pretending to be - a commando who spoke to Le Monde said it looked like "hell". The room was still and silent, he said, but for sound of mobile phones ringing out.
How could such a large-scale attack be planned and carried out without the intelligence services knowing a thing about it? For the authorities, the most galling mystery about the attacks is how they failed to avert them.
Prime minister Manuel Valls has defended the security services, saying they have prevented multiple attacks and that keeping track of the hundreds of French nationals who have gone to join Islamist militant groups in Syria poses huge operational challenges (former president Nicolas Sarkozy says the intelligence watch-list contains 11,500 names).
But the investigation has already revealed that the agencies failed to join the dots. The massacres were carried out by a group that included suspected radicals who were on the watch-list yet somehow managed to procure weapons, produce explosive vests, hire cars, rent apartments and co-ordinate multiple attacks without a red flag appearing anywhere in the system.
All the suspects were known to the police. One, Samy Amimour, had been on probation after attempting to go to Yemen but somehow vanished from the authorities' radar in September 2013. Another, Ismaël Omar Mostefaï, was listed by the intelligence services as a potential threat to national security.
