Vincent Bugliosi's remarkable 20-year work on who killed John F. Kennedy has just been published. Containing about a million and a half words and thousands of footnotes, "Reclaiming History" is probably the most detailed examination of one moment in time ever written. It reconfirms that a man named Lee Harvey Oswald acted alone in killing the American president.

As one who never doubted the original U.S. government report that Oswald acted alone, I am deeply grateful to Bugliosi for the service he has rendered our country. But I also regret that he had to.

Why did he have to? Because it was necessary to definitively refute all those who believe, despite bipartisan government reports and excellent books such as Gerald Posner's "Case Closed," that there was some conspiracy to kill President Kennedy and that Oswald was not the only shooter.

There is not a shred of evidence that there was a conspiracy to kill John F. Kennedy, but that is entirely irrelevant to those who choose to believe that there was one. The lack of evidence only reinforces their belief that a conspiracy has been hidden.

One would think that someone would have come forward in the last 44 years to tell the world about the conspiracy. He or she would become a major figure in history, not to mention the likelihood of becoming very wealthy. But somehow, despite the fact that the government can rarely hide for months even what it wishes to hide, both Democratic and Republican administrations acting in cooperation with each other have hidden these facts.

As Bugliosi pointed out to me, it would in fact have had to be a double conspiracy -- first, the plot to assassinate, and then the plot by a much larger group, including many honorable people involved in the investigation, to cover up the original conspiracy.

Likewise, given the vast amount of planning and implementation -- and the large number of people -- that would have been involved in arranging the 9/11 destruction of the World Trade Center towers and part of the Pentagon, not one person has come forward -- not one American or foreigner, not one leftist or rightist -- to reveal a U.S. government plot to murder thousands of Americans and bring down two of the tallest buildings in the world.

Why, then, do people believe in these and other conspiracies? (Of course, there are known conspiracies -- Osama bin Laden and others conspired in the 9/11 plot -- but there are no successful hidden conspiracies. I cannot think of one in my lifetime.) There are at least six major reasons: Continued...