At the Alfred P. Murrah Federal Building, a quiet spring day began like any other in Oklahoma City on April 19, 1995. Government employees arrived for a busy workday. Parents dropped their children off at the day care center. Suddenly, a colossal explosion tore through the nine-story building, the front of it crumbling to the ground. More than one hundred people died instantly. Many more were injured. Tragedy gripped the nation. What caused the explosion?...