A quick review: In 1964, the Warren Commission concluded that only three shots were fired all from behind the President, all from the Texas School Book Depository, all from the bolt-action rifle of Lee Harvey Oswald. End of story. (Beginning of conspiracy-theory industry.) In 1979, an investigation conducted by Congress's House Assassinations Committee disagreed a fourth shot, which missed, had been fired from behind a white picket fence on that grassy knoll. In 1982, however, a special panel of the National Academy of Sciences insisted the fourth shot was random background noise, probably static.
Now, an article published by JFK assassination researcher D. B. Thomas in Science and Justice, a quarterly publication of Britain's Forensic Science Society, says the NAS study was seriously flawed and the House committee was right.
The source of the disagreements arises from the fact that audio/video technology was a bit underripe in those days; the famed Zapruder film was unmiked, and the primary sound recording available of the events that transpired are from Dallas police transmission channels, recorded when a motorcycle patrolman inadvertently left his microphone on. The House panel was able to use filtering techniques available at the time to isolate "audible events" during a 10-second time frame that it thought could be gunfire and found four.
But the NAS, which was following up on the House committee's work, used two other recordings of Dallas police transmissions from the radio channels the police were using that day, and after matching up the two incomplete recordings and the police reactions therein concluded that the supposed grassy-knoll shot occurred too late to be part of the assassination.
Thomas disagrees. Using a different instance of so-called "cross talk," he determined that the gunshot-like sound from the grassy knoll occurs "at the exact instant that John F. Kennedy was assassinated." Accordingly, he tabulated that there was a more than 96 percent chance that a second gunman took a shot at Kennedy. Not only that, says Thomas, he believes the fourth shot was the one that killed the President.
None of which gets to the really juicy conspiracy-theory stuff, such as whom the shooter on the knoll was working for. But it's certainly not doing Earl Warren's legacy any good.