In a corner of the Shannon Rose Hill Cemetery, close to a chain-link fence that separates the living and the dead, a patch of ground has been worn free of grass by all who come to stare at one particular gravestone. With just a surname, the marker says it all: OSWALD. But in the half-century since a slight, sallow man named Lee Harvey Oswald killed President John F. Kennedy, so much continues to be said about the assassination that the various conspiracy devices and theories are nearly as familiar as the tragic event itself. The Magic Bullet theory. The Zapruder...