Social worker De-Charles Claude Aka sits in his office in the Grande Borne neighborhood of Grigny, France, a southern suburb of Paris. He worked as a counselor to Amedy Coulibaly when the self-proclaimed Islamic State group terrorist was a teenager in the neighborhood. Aka says he lost sight of Coulibaly in 1999. Then suddenly in 2013, his former charge reappeared in his office, seemingly with something important to say. Whatever it was, Aka failed to tease it out of him. He is now haunted by the idea that Coulibaly may already have been plotting last week’s murder-spree, and perhaps could have been reasoned with. Instead, they made small talk.