It's been over forty years since the assassination of president John F. Kennedy, but rumors still abound that a conspiracy was behind it. A new study of the evidence says that's very unlikely.
Vetting a conspiracy theory. I'm Bob Hirshon and this is Science Update.
Many people think Lee Harvey Oswald had help shooting President Kennedy. But that's very unlikely, according to retired atmospheric chemist Ken Rahn. He and ballistics specialist and statistician Larry Sturdivan have re-analyzed the data from two major forensic studies of the assassination.
With good statistical techniques, you can understand what the results are trying to say with a clarity and a force that we don't think was available before.
They showed that despite apparent chemical differences, the tiny bullet fragments recovered from the president's limousine matched the larger bullets found in his body. Those bullets, in turn, have been conclusively matched to Oswald's rifle. Dr. Rahn says the odds of this happening by chance with two shooters are as little as a million to one. I'm Bob Hirshon for AAAS, the Science Society.
Making Sense of the Research
Few historical events are as popular with conspiracy theorists as the JFK assassination. Perhaps it reflects the startling nature of the event: it was hard to believe, especially at that time, that a lone individual could bring down a president (although it had happened three times before). Also, the mystique that surrounded Kennedy and his family has probably added fuel to the fire. Parties as diverse as the Mafia, Fidel Castro, the CIA, the Russians, and even Vice President Lyndon Johnson have been suggested as co-conspirators in Kennedy's murder.
Rahn and Sturdivan didn't conduct a whole new investigation; they just re-analyzed the data from two main studies: the official FBI investigation in 1964, and a 1977 study by Richard Guinn at the University of California at Irvine. Although both studies were basically sound, their data was confusing and difficult to understand, and contained small errors that clouded the finality of their conclusions.
To suggest that more people were involved in the assassination, conspiracy theorists often note that although three shots were fired that day, and the shots that hit the President all occurred within 4.8 seconds, Oswald's rifle could fire only one shot every 2.3 seconds. That would make Oswald unlikely to be the only shooter—IF all three shots actually hit the President. However, Rahn and Sturdivan's analysis show that the first shot probably missed the President's car altogether. That leaves plenty of time for the two shots that did hit to be fired from Oswald's rifle.
Rahn and Sturdivan drew important conclusions about the chemical composition of the bullets found at the scene. They show that the particular brand of bullet Oswald used, manufactured at that particular time, had chemical properties that tended to vary much more widely than most other bullets from the same batch. Specifically, an element called antimony, which is often used as a marker in forensic evidence, distributes itself very unevenly in these bullets.
That's important because there were five bullet fragments found at the scene: two large ones that could be traced conclusively (using ballistics) to Oswald's rifle, and three other fragments that were too small to trace using ballistic evidence alone. Because the proportion of antimony in these bullets varied widely, some people believed they must have been different brands of bullet, and therefore probably from another person's rifle. But Rahn and Sturdivan showed that this variation in antimony is exactly what you would expect for the type of bullets Oswald used. Moreover, they showed that the fragments of bullets found on the ground and in the car chemically matched the bullets found in the President's brain, which were traced, using ballistics, exclusively to Oswald's rifle. This rules out the possibility that someone planted extra bullet fragments at the scene.
The researchers also were able to show, for the first time, the statistical probabilities for popular conspiracy theories. Using the ballistic and chemical evidence from the five bullet fragments, they showed that the chance that another shooter was involved—ASSUMING the shooter used the EXACT SAME rifle and bullets as Oswald—was no more than 2%. When you throw out that extremely unlikely assumption, the chances go down to as small as one in a million. "In other words," says Rahn, "it didn’t happen."
Now try and answer these questions:
- Why did Rahn and Sturdivan conduct this study?
- What did they clarify and rule out?
- Why do you think conspiracy theories exist?
- Can you think of other historical events that have inspired conspiracy theories? How might you test these theories scientifically?
Dr. Rahn maintains The Academic JFK Assassination Site, devoted to scientific analysis of the JFK data.
The Skeptic Society and Skeptic magazine are devoted to the scientific investigation of controversial or extraordinary ideas.