Two teenage girls were arrested in Nice, France, on Sept. 25 for conspiring to conduct terrorist attacks on behalf of the Islamic State. During the interrogation, the young women admitted to authorities that they had been in contact with Rashid Kassim, a 29-year-old French jihadist affiliated with the Islamic State who has been active on Telegram, an instant messaging service. The girls' arrest came 11 days after a 15-year-old Parisian boy was detained for hatching plots at Kassim's behest.
French authorities believe Kassim is responsible for directing a number of grassroots jihadist attacks across the country. Some of the cases he is suspected of being linked to are the June 13 stabbing of a policeman and his partner at their Magnanville home, the July 26 murder of a priest in Saint-Etienne-du-Rouvray and the botched Sept. 7 car bombing near Notre Dame. The spate of assaults Kassim managed to incite demonstrates the...