PARIS -- French police say hundreds of mourners at Republique Plaza apparently panicked after hearing firecrackers and cleared Paris' iconic Republique Plaza, the scene of one of the Friday night's attacks.
In France's 10th arrondissement, near a small Cambodian restaurant and a bar that were the scenes of shooting on Friday night, panic broke out and police broke through with guns drawn.
The two are about a 10-minute walk apart, in the same general area of Paris.
Seven people have been detained in raids in Belgium connected to the Paris attacks, Belgian officials say.
Those arrested were in contact with the Paris attackers, a senior Belgian counterterrorism source tells CNN. No weapons or explosives were found on them.
Europe's worst security nightmare appears to be coming true: At least one of the terrorists who attacked civilians in Paris on Friday entered the European Union hidden among the wave of refugees arriving on European shores.
One of three bombers who detonated himself at the Stade de France late Friday arrived on the Greek island of Leros on October 3 among numerous Syrian refugees, CNN's Christiane Amanpour reported, citing an unnamed French senator who was briefed by the Ministry of the Interior.
The man declared himself to be Syrian, said his name was Ahmad al Mohammad and was, under new procedures set up to help refugees, issued a new emergency passport.
From Leros, he traveled to Macedonia, Serbia and then Croatia, Amanpour reported.
The fingerprints from the bomber at the Stade de France match those taken when the man was issued his emergency passport on Leros.
The two others who detonated themselves at the stadium carried false Turkish passports, Amanpour reported.
It appears that the Islamic extremist group ISIS is making good on its pledge to hide operatives among the tide of legitimate refugees now entering Europe.
European officials believe, Amanpour said, that there is "a very professional new squad of terrorists inserting themselves into some of these migrant voyages."
ISIS has claimed responsibility for Friday night's coordinated series of deadly assaults, the worst violence in France since World War II.
Three Kalashnikovs found in abandoned car
Beyond that, investigators in France and beyond have begun making arrests as they piece together the identities and backstories of the terrorists who killed more than 120 people in gun and bomb attacks across Paris.
The clues and evidence appeared Sunday to be piling up. The French channel BFMTV, a CNN affiliate, reported that authorities had found three Kalashnikov automatic rifles in an abandoned car in the eastern Paris suburb of Montreuil that was believed to have been used by perpetrators of the attacks.
But officials are still trying to figure out who the assailants were and how they planned and carried out near-simultaneous massacres at restaurants, bars and a concert hall in the French capital without being detected beforehand by intelligence agencies.
One of the suicide bombers has been identified as Ismael Omar Mostefai, according to Jean-Pierre Gorges, the mayor of the French town of Chartres, who is also a member of Parliament. Mostefai lived in Chartres at least until 2012, Gorges said in a Facebook post Saturday.
One attacker identified as French
The news agency Agence France-Presse reported that Mostefai was the same attacker who was described Saturday by Paris prosecutor Francois Molins, something CNN has not confirmed independently.
Molins, who did not identify the attacker by name, said he was a 29-year-old French citizen with a criminal record from the southern Paris suburbs.
The attacker was involved in the assault and hostage-taking at the Bataclan concert hall, where the highest number of people were killed Friday, according to the prosecutor.
The man, who was identified by fingerprints, was believed to have been radicalized in 2010 but had never been accused of terrorism, Molins said.
Agnes Thibault-Lecuivre, the Paris prosecutor's spokeswoman, told CNN that six people -- all family relatives of Mostefaï -- have been detained.
It is common practice in criminal cases in France to place family members in custody. Mostefaï's relatives have not been charged or arrested.
Raids in France, Belgium
As investigations into the attacks gathered speed over the weekend, authorities detained people in France and Belgium.
In Belgium, raids were conducted in a Brussels suburb, Justice Ministry spokeswoman Sieghild Lacoere said. A car rented in Brussels was found near one of the sites of the Paris attacks, which triggered the raids, Lacoere said.
At least one of the raids was connected to the Paris attacks, according to a Western intelligence source who is in contact with French and Belgian intelligence services. The other raids were connected to people known to Belgian intelligence, the source told CNN.
Some of the Paris attackers were also known to Belgian intelligence, the source said.
Also Saturday, CNN affiliate BFMTV reported that the father and a brother of one of the attackers had been taken into custody. And AFP reported that the two men were detained after police raided their homes 130 kilometers (80 miles) east of Paris. CNN has not independently verified that the men were picked up by authorities.
A man who rented a VW Polo used by terrorists at the Bataclan was intercepted at the border with Belgium, according to Molins, the Paris prosecutor. The man, who was driving a different vehicle when he was caught, is a French citizen living in Belgium and was accompanied by two other people, Molins said.
'An act of war'
"The skies have been darkened by the horrific attacks that took place in Paris just a day and a half ago," U.S. President Barack Obama, in Turkey for a meeting of the G20 group of countries, said Sunday in a joint media appearance with Turkish President Recep Tayyip Erdogan.
"As a NATO ally, we have worked together to bring about pressure on ISIL even as we also try to bring about a political transition inside of Syria that can relieve the suffering of so many people and eliminate the environment in which ISIL can operate," Obama said. ISIL is another acronym for ISIS.
The G20 leaders are expected to focus largely on terrorism in the wake of the attacks in Paris.
French President Francois Hollande has called the shootings and bombings, some of which targeted an international soccer game he was attending, "an act of war." He has vowed merciless revenge on ISIS, which France is already bombing in Iraq and Syria as part of the U.S-led coalition against the militant group.
The French government has declared a state of emergency and announced three days of mourning for the victims of Friday's bloodshed.
But many leaders seem to agree that Friday's attacks in Paris mean the threat to many Western countries has increased.
In the UK on Sunday, British Home Secretary Theresa May is set to chair a meeting of the Cobra crisis response committee in London. Prime Minister David Cameron is in Turkey for the G20. Cobra meetings are held to discuss urgent security matters and include senior figures from the British government and heads of intelligence and security agencies.
The violence that hit six different sites around Paris has deepened the trauma for Parisians, who had already been shaken by a series of terrorist attacks in January that left 17 people dead.
People were still out around the city Saturday, some posing for selfies along the Seine or stealing a kiss in front of the Eiffel Tower. But the tower itself -- like many other tourist attractions, shops and public buildings -- has been closed in the aftermath of the attacks.
Fears the terror isn't over
Security has been stepped up, with military reinforcements drafted in.
There has been an outpouring of support and solidarity in Paris, but large gatherings in the streets have not materialized, partly because the state of emergency prohibits them.
Sadness and fear are taking a toll, Paris Deputy Mayor Patrick Klugman said.
"We don't know yet if this terror in fact is over or not," he told CNN, highlighting the jitters caused by unsubstantiated rumors circulating on social media.
In addition to the 129 people killed in Paris, 352 were injured, at least 99 seriously, Molins said Saturday.
The dead include many French citizens, three Chileans, two Belgians, two Mexicans, two Spaniards, two Portuguese, an American and a Briton.
In an online statement distributed by supporters Saturday, ISIS said eight militants wearing explosive belts and armed with machine guns attacked selected areas in the French capital.
Seven of the terrorists were killed, mostly by blowing themselves up, according to French officials. The attackers are believed to have operated in three teams.
U.S. officials say they are waiting for corroboration from DNA and fingerprint tests to help positively identify the attackers, something that will take some time.
The FBI is running through databases an initial batch of names that could be those of the attackers or people associated with them, according to U.S. law enforcement officials. So far none of those names are known to the United States as terrorism suspects, the officials said.
The scale and coordination of Friday's wave of deadly assaults inside a major Western city -- coming soon after ISIS' claim of taking down a Russian airliner in Egypt -- appear to represent a deeply disturbing increase in the extremist group's capabilities.