A Syrian passport found by police at the scene of the mass shooting in a Paris concert hall belonged to an asylum seeker who registered on a Greek island in October, a Greek minister said Saturday.

“We confirm that the Syrian passport holder came through the Greek island of Leros on October 3 where he was registered under EU rules,” said a statement issued by Nikos Toskas, the minister for citizen protection.

French police said the document was found “near the body of one of the attackers” in the investigation into the main attack of Friday’s carnage, at the Bataclan concert hall, where 82 people were killed. That attacks was one of six coordinated shootings and suicide bombings that left no less than 128 murdered in Paris.

Police are not ruling out that the passport changed hands before the attacks.

“The most logical assumption is that it’s the same person, sent on a mission to Europe,” said a European security expert speaking on condition of anonymity. “If this is established, it would be the first such case. In any event, this proves that the unchecked flow poses an unequaled challenge for European security. We simply don’t know who is coming through.”

The Greeks were also examining a fingerprint from a second assailant provided from Paris, to check whether this person had also come through Greece, the police source said.

In recent weeks there has been a storm in Europe over the building migrant crisis as hundreds of thousands of Middle Easterners flood the borders of European countries. Many have spoken out against letting in the migrants out of concerns that terrorists would easily be able to infiltrate their midst and enter Europe to conduct large-scale attacks, such as those seen Saturday.

Greece’s junior minister for migration Yiannis Mouzalas had admitted in September that it would be “foolish” to completely discount the possibility of jihadists sneaking into Europe among the refugee wave.

Over 800,000 people have crossed the Mediterranean to Europe this year, with over 3,400 dying in the process.

Mouzalas noted that the number of Europeans joining extremist groups in the Middle East was in fact far higher. “The opposite is happening. They leave from here and go over there,” he said.

But Prime Minister Alexis Tsipras on Saturday insisted that the refugees fleeing Syria “are hunted by the same terrorists” that struck in Paris on Friday.

“We must find solutions to the drama of the people who leave their homes, hunted by the same terrorists, and drown in the Mediterranean,” Tsipras said in a televised address.

It remains to be seen what if any impact the revelation of the passport in the Paris attack will have on European policy.

AFP contributed to this report.