A Syrian passport found at the scene of the Paris attacks matched that used by a refugee who arrived on the Greek island of Leros last month, the Greek deputy public security minister said last night (Saturday).
The statement, made after French police shared details with European intelligence agencies of the clues they had picked up so far as to the killers' identities, is the first link to a terrorist attack from the waves of migrants heading across the continent.
Experts warned that the passport could have been stolen or bought in a well-established black market. But if one of the terrorists masqueraded as a migrant, it will be a development long feared both by European governments, aware that the hundreds of thousands of people arriving from Syria, Iraq and Afghanistan were likely to include security risks, and refugee agencies, afraid of a popular backlash.
"We announce that the passport holder passed through Leros on 03.10.2015 where the identity was checked under EU rules," the minister, Nikos Toskas, said. "We do not know if the passport was checked by other countries which the holder is likely to have passed through."
The Paris prosector said seven attackers were killed, all of them in suicide bombings - a new tactic in France and the first such attack since the 7/7 bombings in London. Four died at the Bataclan concert hall, one on the Boulevard Voltaire near the venue, and three at the stadium.
One Syrian passport is thought to have been found near the body of one of the bombers at the Stade de France. The owner of an Egyptian passport which was also found near a body at the stadium was later understood to have been traced to a spectator at the game who is being treated in hospital and not regarded as a suspect.
At least one of the suspects, believed to have blown himself up inside the Bataclan, was a 30-year-old Frenchman, flagged as an extremist in 2010, and known to intelligence services.
Police did not disclose his identity in case it hindered the investigation, but his fingerprints were found on bullet casings.
Reports suggested two of the attackers were Belgian. One witness said he saw two black cars, of which one carried a Belgian number plate, and police were searching addresses in Molenbeek, Belgium, after police found a parking ticket from the city on a suspect's car.
The authorities said they had made three arrests. "There were arrests relating to the search of the vehicle and person who rented it," Koen Geens, the Belgian justice minister, said.
Some evidence points to the attack having been planned in Syria, where the town of Raqqa has become the de facto capital of the so-called "Caliphate" of the Islamic State of Iraq and the Levant (Isil). It is also where a drone strike on Friday reportedly killed Jihadi John.
An anti-Isil activist living in Deir Ezzor, a town partly held by Isil between Raqqa and the Iraqi border, told The Sunday Telegraph that earlier this year he overheard foreign fighters plotting a "huge" terror attack in Paris from an internet cafe.
Tim Ramadan, who works with the group "Raqqa is Being Slaughtered Silently", said a fighter using the nom-de-guerre Abu Ibrahim al-Belgi - "father of Ibrahim, from Belgium" - was speaking to a "commander" who gave the orders for an attack.
"He said two (fighters) were sent in March and two more would be sent in May," Mr Ramadan, speaking under a pseudonym, said. "They were saying goodbye and were going on an operation to France."
Likewise, in August, a Frenchman arrested on his return from Syria after a short stay in Raqqa mentioned instructions from Isil to target a concert hall.
"Isil videos contained references to France within the past week and there is some suggestion that they were a signal to a possible cell already inside the country," one source said.
France is part of the US-led coalition that has been striking the Islamic State group in Iraq, and more recently Syria. It has been targeted by jihadists in the past because of its perceived tolerance of speech deemed offensive to Islam.
France and Belgium have the highest number of western European fighters with Isil in Syria and Iraq.
Isil's online statement said seven militants armed with explosive belts and automatic weapons attacked carefully chosen targets in the "capital of adultery and vice". It referenced the stadium, and the Bataclan, where an American rock band was playing, and said "hundreds of apostates were attending an adulterous party".
The statement said France and its supporters would "remain at the top of the list of targets of the Islamic State".
Police said the attackers were "seasoned fighters by the looks of it and perfectly trained, with witnesses describing them as quite young and cool-headed".
An estimated 520 French nationals are fighting in Syria and another 250 have returned to France, officials said.
The gunmen's bodies have been taken to Paris' institute of forensic medicine for DNA checks.