Story highlights None of the individuals identified so far in the Paris attacks have been on any U.S. watch-lists

U.S. investigators are increasingly convinced the attackers used encrypted communications to evade French intelligence

(CNN) Multiple U.S. officials tell CNN none of the individuals identified so far in the Paris attacks have been on any U.S. watch-lists, raising new questions about how effectively the U.S. and its allies are able to track foreign fighters traveling to Syria and Iraq.

U.S. intelligence analysts have also been combing through signal intelligence, including email and other communications, and have turned up no communications among the attackers. This is partly why U.S. investigators are increasingly convinced the attackers used encrypted communications to evade French intelligence.

One U.S. official described it as an "educated presumption." Two U.S. officials said that view is based partly on the fact that at least one of the attackers at the Bataclan theater, who French authorities had already identified as radicalized before the rampage, was known in the past to have used popular encrypted apps.

U.S. investigators also say they still don't know definitively whether there are more operatives involved in the attack who may be at large. French officials have told CNN they believe there are.

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U.S. officials say the scale of the Paris attack has overwhelmed French investigators. "As you can imagine, it's very -- still very chaotic there to get some of the information," Diego Rodriguez, assistant director for the FBI's New York field office, said Monday. "What we do is when we send folks over there, we -- we send them over there so that they can work in collaboration with our legal attaché, who is working with the local police departments, just like we would do here." Over the weekend, the FBI sent additional agents to France to join the personnel already based in Paris in case assistance was needed, but so far France has not formally asked the FBI to join the investigation.

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