An official with the Paris prosecutor's office said investigators questioning the 16-year-old found evidence of regular visits to jihadi sites and of "incitement to terrorism," but that the minor's case had been handed over to prosecutors in the nearby city of Rouen who cover the region.
She spoke on condition of anonymity as she was not allowed to be named publicly.
Judicial authorities in Rouen did not immediately return a message seeking comment.
The Islamic State group claimed responsibility for the attack, as well as the July 14 truck attack in Nice, where 84 people were killed by a man who plowed a truck down a seaside promenade. France has seen rising jihadi violence in the past 18 months, with attacks against journalists, Jews, police and partygoers.
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In a separate development, two men suspected of connections to the Paris attacks were extradited yesterday from Austria to France. The men, identified by Austrian authorities as a 35-year-old from Pakistan and a 29-year-old from Algeria, are believed to have come to Europe last year posing as refugees. French authorities have said the men were handed preliminary charges of "criminal terrorist association."
In yet another development, the official with the Paris prosecutor's office said that an unnamed man detained in the wake of the Nice truck attack would be sent to Paris on Monday, a step toward preliminary charges.