Almond and pear trees are in blossom on the drive into Ibrahim Zahar, a tiny and picturesque collection of perhaps a few dozen houses in Kasserine, one of the poorest regions of Tunisia. A handful of mourners gathered at its hilltop cemetery this week for the funeral of a once promising young man who had hoped to study for a degree in philosophy. But most residents stayed away. Jabeur Khachnaoui, the 20-year-old school student whose body was quietly buried on Monday, might never have been known beyond Kasserine had he and a fellow gunman not burst into the Bardo Museum in Tunis to slay as many foreign tourists as they could before the police shot them dead. The attack was planned by the...