Early leads in the investigation into the deadly Paris attacks point to the likelihood of a team led by French nationals, based in Belgium, and which may have used a refugee route from Syria via Greece to link up for their killing spree.

Details are only slowly emerging of the seven dead attackers and an eighth assailant still on the run who perpetrated strikes on Paris bars, a concert hall and a soccer stadium that killed 132 people and injuring 349.

But elements pieced together so far suggest a well-organised and trained multinational commando team, backed by an equally cross-border network reaching from the Middle East to Brussel’s rundown suburbs, via the Greek island of Leros and the French cathedral town of Chartres – and possibly involving Germany.

The international reach of their network prompted French Interior Minister Bernard Cazeneuve to call for an urgent European Union meeting to assess what new security measures the bloc needs to counter such threats.

“The abject attack was prepared overseas, mobilised a team based on Belgium territory and benefited from support in France,” he told a news conference with his Belgium counterpart.

Four of the eight attackers which Islamic State said it had sent to do the killings are now known to have been French nationals, including Ismael Omar Mostefai, a 29-year-old of Algerian descent from Chartres, southwest of Paris.

He is one of seven militants who died in the slaughter, blowing himself up at the Bataclan musical hall, the bloodiest of Friday’s attacks.

His profile is typical of French jihadists — a period of petty crime before he became quickly radicalised and withdrew from the social circle he had previously known.

French media cited local residents as saying he had been influenced by a visiting radical Imam from Belgium in 2010, the same year that the Paris prosecutor said his security file for Islamist radicalisation was created.

Quoting unnamed sources, Le Monde daily reported the father-of-two had likely travelled to Syria in the winter of 2013-2014 before returning to Chartres.

The only other named member of the network so far is also French, Belgian-born, and still on the run. Salah Abdeslam is 26 and suspected of having rented the black VW Polo car used during the shootings, French police said.

The Paris prosecutor’s office has identified another two of the dead attackers as French nationals. It did not given their names, but said they were suicide bombers, aged 20 and 31, at the Stade de France stadium and one of the bars. A judicial source said one of the two was a brother of Abdeslam.

All Roads Lead To Belgium

Indeed it is in Belgium, the EU state which proportionate to its population has contributed most foreign fighters to the civil war in Syria and which has figured in several Islamist attacks and plots across the continent in the past year, where investigators are making fastest progress.

Belgian prosecutors said on Sunday seven people had been detained following raids and also confirmed the two French suicide bombers had been living in Belgium.

Of those arrested, at least one of those held from the inner Brussels neighbourhood of Molenbeek was believed to have spent the previous evening in Paris, where two cars registered in Belgium were impounded close to scenes of some of the violence.

“I ascertain that there is nearly always a link with Molenbeek, which is a gigantic problem,” Belgian Prime Minister Charles Michel said.

The Migrant Link

While the French and Belgian links look strong, the direct connection to Syria and the Middle East is harder to pin down.

The holder of a Syrian passport found near the body of one of the suicide bombers near the Stade de France, the national stadium, was registered as a refugee in Greece and Serbia last month, after travelling through the Greek island of Leros, where he was processed on Oct. 3. Greece identified the man as 25-year old Ahmad Almohammad from the northwestern Syrian city of Idlib.

France has not publicly confirmed that the passport-holder is a suspect, but Greek Migration Minister Yannis Mouzalas said French authorities had told Greece they suspected Almohammad, whose passport was found outside the Stade de France near the body of a gunman, was indeed one of the attackers.

Such a connection, if proven, would be particularly sensitive because if a killer did enter Europe among refugees and migrants fleeing war-torn countries, this could change the political debate about accepting refugees.

Jihadi sources told Reuters in September they were using the migrant crisis to send some of their fighter to Europe, although Western officials played down that prospect.

It is also possible Islamic State may have wanted to leave a Syrian passport behind to stoke fears about migrants in Europe.

“It can be that a terrorist was infiltrated there (through the refugee route). It can be that this trail was laid on purpose by the IS to influence the refugee debate,” German Interior Minister Thomas De Maiziere told German television.

Others suggest the passport may be fake.

“Such fake Syrian passports are widely available in Turkey, and are often bought by non-Syrians trying to get to EU because Syrians get preferential treatment on the journey,” Human Rights Watch’s Peter Bouckaert, a close Syria-watcher, wrote on his Facebook page.

With investigators trying to trace back the origins of weapons and explosives used in the attack, the list of countries used by the cell may well increase.

A man arrested in Germany’s southern state of Bavaria in early November after guns and explosives were found in his car may be linked to the Paris attacks, Bavaria’s state premier said on Saturday.

Analysis of the Montenegro man’s car navigation system found he drove from Montenegro via Croatia, Slovenia and Austria to Germany, aiming to reach France. Asked about his destination, the man said he wanted to see the Eiffel Tower, police said.

Criminologist Alain Bauer, a former security adviser to French ex-president Nicolas Sarkozy, said the increasingly coordinated character of much European criminal activity was not always matched by the work of police authorities.

“We have a series of European partners that have completely different policies, be it on terrorists or organised crime,” he said.