Fifty years after the assassination of President John F. Kennedy, 59 percent of Americans still believe it was the work of a conspiracy. I was once among them. Back in the early 1970s, as a high school senior and college freshman, I read Mark Lane's Rush to Judgment, Richard Popkin's The Second Oswald, Penn Jones' Forgive My Grief, and other tomes, some of them best-sellers, that argued the case for a dark plot.