Following is a summary of what is known so far about Friday's attacks in Paris that left at least 128 murdered:
Islamic State claim
The Islamic State (ISIS) jihadist group has claimed responsibility for the attacks. It said "eight brothers wearing explosive belts and carrying assault rifles" conducted a "blessed attack on... Crusader France."
Clues to the attackers
The main lead for French police is a Syrian connection. A Syrian passport was found near the body of one of the assailants and police believe members of the group may have trained in Jihadist areas. The attackers seemed to be fit and well-trained, a police source said.
Witnesses say they were young and very self-assured. Police identified a Frenchman, previously known to police, as "very likely" being one of the assailants.
One or more of the attackers shouted out in French, which points to others also being French nationals.
Authorities hope DNA tests and fingerprinting on the attackers' corpses will yield further clues.
A foreign base?
Witnesses say the attackers drove up in a Belgium-registered car. This may mean the group operated from outside France, but police are not ruling out local support. Another pointer to foreign involvement is the arrest of a man in Bavaria, Germany, carrying automatic weapons and explosives, who could have a link to the Paris attacks, according to a Bavarian minister.
The simultaneous attacks on the Stade de France during an international match, on restaurants and a concert hall - all within 30 minutes - carry the hallmarks of a masterminded assault to spread fear and confusion. In August, a Frenchman arrested on his return from Syria, where he spent time in the Islamic State stronghold of Raqqa, mentioned an ISIS order to target a concert hall, according to a police source.
Investigators into terrorist attacks in January, which targeted the satirical magazine Charlie Hebdo and a Jewish supermarket, say the assailants received instructions from the Iraqi-Syrian border region controlled by ISIS.
The modus operandi: A first for France?
These attacks differ from previous ones in France, in their scale and operational style, say investigators.
Suicide vests in particular are a first. French police say this points to a highly-skilled bomb maker still at large.
"An explosives expert never takes part in attacks, he is too valuable for that. So he's out there somewhere," former intelligence chief Claude Chouet told AFP.
France is throwing everything it has into the probe. All investigating judges are on alert. All French anti-terror units have been mobilized. The entire force of the so-called Judicial Police specializing in criminal probes, totaling 2,000 agents, has been deployed.
The state of emergency declared by President Francois Hollande gives police wide powers, especially for night raids. Anti-terror judges are standing by.
France has asked for assistance from foreign intelligence services, especially in Europe.
AFP contributed to this report.