S HAMSUD-Din Jabbar , a 42-year-old American citizen and military veteran from Texas, had worked as an IT specialist in the army and praised the discipline and planning that it taught him. He had a conviction for theft. Why he rammed a rented Ford pickup truck into a crowd of revellers on Bourbon Street in New Orleans in the early hours of January 1st, killing at least 14 and injuring 35, is mysterious and in a sense always will be.