PARIS — When Chérif Kouachi first came to the attention of the French authorities as a possible terrorist a decade ago, he was in his early 20s and, according to testimony during a 2008 Paris trial, had dreamed of attacking Jewish targets in France. Under the influence of a radical Paris preacher, however, he decided that fighting American troops in Iraq presented a better outlet for his commitment to jihad. On Wednesday, Mr. Kouachi, according to investigators, returned to his original plan of waging holy war in France. Along with his older brother Said and a third French Muslim of...