Authorities say as many as 20 people may have been involved in the plot to attack Paris. Here's what we know about them so far. (Gillian Brockell/The Washington Post)

Could Europe’s migrant trail become a militant trail?

It’s a question being asked after French prosecutors confirmed Monday that the fingerprints of one of the Paris suicide bombers matched those of a man who passed through Greece last month. That was the clearest sign yet that one of the attackers blended in among the hundreds of thousands of refugees and migrants who have arrived in Europe this year.

The news is adding fuel to an already heated debate in Europe over how to handle the massive influx of migrants to the continent.

Officials believe that eight assailants were directly involved in the coordinated attacks Friday that left at least 129 dead. Five have been identified as French nationals, two have not been named, and the identity of the last one remains a mystery.

He blew himself up outside a soccer stadium north of Paris, and a Syrian passport was found near his body in the name of Ahmad Almohammad. French prosecutors stressed it had not been authenticated, leaving open the possibility that it was a fake. Greek authorities have said that a man carrying a passport with Mohammad’s name was registered along with other migrants on the Greek island of Leros on Oct. 3.

Leader of the French far-right party Front National (FN) Marine Le Pen called Monday for an “immediate halt” to France’s intake of migrants, adding that “our fears and warnings about the possible presence of jihadists among migrants” entering the country had proven to be true. (Thierry Chesnot/Getty Images)

But while the man’s identity remains unclear, his fingerprints connect the terrorist attacks to the migrant trail stretching from the Mediterranean into central Europe.

That linkage could imperil attempts by the European Union to come up with a coordinated policy to address the migration crisis. Even before the Paris bombings, there was a growing backlash in Europe against the record number of asylum seekers pouring through Greece and across the Balkans. Some politicians cited concerns that militant groups such as the Islamic State would slip members into Europe via the route refugees have taken through Greece and the Balkans.

On Monday, Marine Le Pen, leader of France’s far-right National Front party, called for an “immediate halt” to France’s intake of more asylum seekers, adding that “our fears and warnings about the possible presence of jihadists among migrants” entering the country had proved to be accurate. Her party took nearly 18 percent of the vote in the first round of the presidential election in 2012 and could make major gains in upcoming regional elections.

In a speech on Monday night, Nigel Farage, the leader of the anti-immigrant U.K. Independence Party, said that Europe’s dream of free movement has resulted in the “free movement of jihadists.” His party won about 13 percent of the vote in national elections this year.

“For those of us who work on refugee issues, this is something we have been afraid of for a while: What would happen to public perception if there was a terrorist attack in Europe?” said Alexander Betts, an expert on migration issues at the University of Oxford.

He added that the “big silent majority” in Europe “want to be compassionate to refugees and asylum seekers, but their support for asylum and immigration is fragile.”

Robin Niblett, director of Chatham House, a London-based think tank, said the revelations could have significant consequences for the Schengen Agreement, a treaty that eliminated internal border checkpoints within Europe.

“Ultimately, in Europe, national governments are responsible for people’s security, not the E.U., and if it looks like the E.U. is a source of insecurity, then Schengen could be largely suspended and not come back into practice until things are fixed,” he said.

European Commission President Jean-Claude Juncker on Sunday urged world leaders not to mistake genuine asylum seekers for terrorists. He said that those behind the bloody nightmare that unfolded Friday were “exactly those who the refugees are fleeing,” adding that “there is no need to revise the European Union’s entire refugee policy.”

The E.U. has proposed to resettle 160,000 migrants across member states. But that was already proving a hard sell in some countries before the attacks.

Poland’s new European affairs minister, Konrad Szymanski, wrote on the news site wPolityce.pl over the weekend that Poland would no longer be able to accept its share of migrants. “In the face of the tragic acts in Paris, we do not see the political possibilities to implement [this],” he wrote.

Hungarian Prime Minister Viktor Orban erected barbed wire fences at the border over the summer after thousands of migrants had passed through. According to news reports, he told parliament in Budapest on Monday that it was “bad even to think about how many terrorists may have gone through the territory of our country.”

German Chancellor Angela Merkel’s coalition partners have criticized the country’s welcoming approach to the migrants and refugees. Germany is expecting to receive more than 1 million asylum seekers this year.

Shortly after the attacks, the finance minister of the German state of Bavaria, Markus Söder, tweeted: “#ParisAttacks change everything. We must not allow illegal and uncontrolled immigration.”

But early signs suggest that Merkel is standing firm. At a news conference Monday, she emphasized that the majority of refugees were “fleeing terrorism.”

Josef Janning, head of the Berlin office of the European Council on Foreign Relations, said it’s likely that Merkel will stand her ground. “She cannot make a U-turn now; this would harm her credibility.”

Concerns were also voiced outside Europe, including in Canada, where provincial and municipal politicians questioned the new government’s ability to conduct effective safety checks on 25,000 Syrian refugees it promised to take by the end of the year.

In a news conference in Turkey, President Obama spoke about the need to support refugees, saying it was important to avoid “equating the issue of refugees with the issue of terrorism.”

Read more:

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Along the migrant trail, pressure grows to close Europe’s open borders