In William Cooper’s book “Behold a Pale Horse PDF” (published in 1991) stated that President Kennedy was actually shot by his limousine driver. Cooper’s conjecture seems to stem from the fact that Secret Service agent William Greer was seen turning to the right and looking back during the shooting.
Of course, there is no clear evidence that Greer was a sniper, though he was heavily criticized after the assassination for not immediately speeding out of the scene that day.