A fatal flaw to many conspiracy theories, especially those that revolve around the medical evidence and the autopsy, is the number of people that would have had to be involved in such a conspiracy — not dozens, but literally hundreds. And one of the conspirators would have to be possibly [first lady] Jackie Kennedy, since she was asked on the flight back to Washington what hospital [she wanted] the president to go to for the autopsy. And she said, "Jack was a Navy man, let's go to Bethesda." So either she knew to pick Bethesda, or you had teams of fake autopsy doctors, ready to do the conspiracy at any number of hospitals in the Washington area that she might have selected. I find that's possible in Hollywood, but not in real life.
ABCNEWS: In the program, one of Lyndon Johnson's closest advisers, Joseph Califano, reports that President Johnson believed that Castro was behind the Kennedy assassination. Why do you disagree?
Posner: Lyndon Johnson makes the mistake that many Americans do. He finds somebody who has a reason to want Kennedy dead, in this case, Fidel Castro, and assumes that Castro was involved. But, because of Oswald's pro-Castro involvement, because of the fact that the month before the assassination Oswald was in Mexico City, visiting the Cuban Embassy, asking to go to Havana, it gives some plausibility to the idea he was acting on behalf of Cuba.
I must say that it's very unlikely that the longest term surviving ruler in the world today, the man who was running Cuba at the time that Dwight Eisenhower was president of the United States, has done so by making such fundamental great gambles as killing the president of the country next door to him, who could eliminate and flatten his entire island in a split second, and do so by relying on somebody as unstable as a 24-year-old sociopath like Lee Harvey Oswald.
Castro is no one's fool. If he had selected someone to shoot the president of the United States, the last thing that that individual would have is a history of being a pro-Castro supporter.
ABCNEWS: Can we ever be 100 percent certain of what happened in the Kennedy assassination?
Posner: If the American public wants 100 percent certainty on who killed JFK, they're never going to come to a conclusion on this case. The best you can do is examine the credible evidence, and reach a conclusion about what likely happened on that day in Dallas 40 years ago. The overwhelming evidence is that Lee Harvey Oswald killed Jack Kennedy for his own reasons, without any conspiracy being involved.
But, anybody looking for 100 percent certainty on that answer, on any controversial area of history, is just not going to find it. The Kennedy assassination is no different.
Gerald Posner is an investigative journalist who is also a trained attorney. He is the author of Case Closed: Lee Harvey Oswald and the Assassination of JFK (1993), and Killing the Dream: James Earl Ray and the Assassination of Martin Luther King, Jr. (1998). His most recent book is Why America Slept: The Failure to Prevent 9/11 (2003).