- 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
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.
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.
The source told CNN that investigators now believe that fireworks detonators bought by Salah Abdeslam in the outskirts of Paris in October were not used in suicide vests. The source said authorities had not yet identified two of the stadium attackers or the other man killed in the Saint-Denis residence in addition to Abaaoud, but identification efforts were still underway.
Earlier this week, CNN reported that based on DNA evidence, investigators had concluded that Abdeslam wore the discarded suicide belt found in a Paris suburb 10 days after the attacks.
He remains at large.
Given that Abaaoud had been one of Europe's most wanted men since January for his suspected role in coordinating a terrorist plot thwarted that month in Verviers, Belgium, it would have been difficult for him to return to Europe legally without being arrested.
Abaaoud had been in touch with the Verviers plotters in January by phone from Greece, a senior Belgian counterterrorism official told CNN previously.
ISIS claimed he returned to Syria after evading an international dragnet in the days that followed a raid on a terrorist safe house in Verviers.
The French newspaper Le Parisien
was the first to report that French investigators had reason to suspect Abaaoud had passed through Leros.
The source also added that no evidence has so far come to light that the attackers used drugs.