As investigators combed through evidence in the wake of the Paris attacks, focus intensified on a Syrian passport found near the body of one of the six attackers who detonated their explosive belts during Friday's attack that left 129 people dead.
A seventh attacker was shot dead by police during a raid on the Bataclan concert hall, where 89 of the victims were gunned down during an Eagles of Death Metal show.
A Greek government official said on Saturday that the Syrian passport had been used to cross into the European Union via the island of Leros in October.
But during Sunday's G20 Summit in Turkey, in which world leaders discussed the threat of ISIS infiltrators among migrants and refugees, Jean-Claude Juncker, the EU chief, urged caution until more is known about who the passport belonged to.
"We should not mix the different categories of people coming to Europe," he said. "The one responsible for the attacks in Paris...he is a criminal and not a refugee and not an asylum seeker."
Facts We dont know yet if gunman is holder of Syrian passport. We know Syrian Passport found in #Paris is for a refugee recorded in #Greece.— Jenan Moussa (@jenanmoussa) November 14, 2015
The Serbian newspaper Blic published a photograph that identified its holder as Ahmad al-Mohammad, 25, a native of Idlib, Syria.
It has not been confirmed whether the passport is genuine or whether it belonged to an attacker, a victim or someone else.
Peter Bouckaert of Human Rights Watch cautioned in a Facebook post on Saturday that fake Syrian passports abound.
"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," he wrote.
Indeed, an investigation in September by the Wall Street Journal showed just how easy it is to obtain fake Syrian documents.
Syrians make up a huge portion of Europe's refugees and, because of the brutal civil war in their country, often receive preferential treatment when it comes to applying for asylum in Europe.
Because of that, other refugees and migrants have been known to try to pass themselves of as Syrians by ditching their original documents and buying stolen or forged Syrian passports which can fetch several thousand dollars on the black market.
Reports on Saturday said that an Egyptian passport had been also been found near the Stade de France during Friday's Germany-France match. But that belonged to an Egyptian victim named Waleed Abdel Razik, according to reports and the Egyptian ambassador to the U.S.
Meanwhile, some have expressed skepticism that the Syrian passport would be intact after the explosion of a suicide bombing.
Why would a jihadist who expressly rejects all notions of modern citizenship take his passport on a suicide mission? So it gets found.— Charlie Winter (@charliewinter) November 15, 2015
The #Syria|n passport is resistant to explosions, fire, bullets, and all the elements, but can't get you into any country. It's amazing!— Dima Moussa (@dimam78) November 15, 2015
As many have noted, strange terrorists took own passports to massacre. Market for Syrian passports is massive. Let's wait for authorities— Matina Stevis (@MatinaStevis) November 14, 2015