Story highlights Source: Paris ringleader was in Greek island of Leros

It is not known whether Abaaoud exploited the refugee processing system

Abaaoud was one of Europe's most wanted men from January until his death in raid

(CNN) French authorities now firmly believe that Paris attack ringleader Abdelhamid Abaaoud, a Belgian-Moroccan ISIS operative, was on the Greek island of Leros some weeks before the terror attack, a source close to the investigation told CNN.

Authorities had previously disclosed that two of the stadium attackers, who have yet to be identified, transited on October 3 through the island, where they used fake Syrian passports to be processed as asylum-seekers.

The source said authorities were investigating whether Abaaoud also took advantage of the refugee processing system to cross back into Europe via Leros, but this was not yet known.

Abdelhamid Abaaoud

Abaaoud was killed in a raid on an apartment in the Paris suburb of Saint-Denis six days after the November 13 Paris attacks.

The source also revealed new details about the attack inside the Bataclan concert hall. There were three attackers inside the hall. After one of the attackers was killed by French police in the initial response, the remaining two gunmen took turns firing at the concertgoers. While one fired, the other reloaded in a systematic way, the source said.

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