Since this thread is called “JFK’s Head Snap and the implausible jet effect…… I thought I would focus on that.
Dr Luis Alvarez, Nobel Prize winner in physics in 1968, did an experiment with a watermelon. Please go to this site
http://www.jfklancer.com/galanor/jet_effect.html and look at the pictures of the watermelon when hit by a frangible round. I know, a head is not a watermelon but they are similar, hard on the outside and soft on the inside. Click on the pictures to enlarge for better viewing. So what happened to the watermelon, the front of it exploded similar to JFK and it was thrown backwards in the direction of where the shot originated.
Now remember in the motion picture “JFK”, Kevin Costner kept repeating when explaining JFK’s head movement “back and to the left, back and to the left, back and to the left”.
Now if you consider Dr. Luis Alvarez's melon experiment the movement of the watermelon went directly back towards where the shot came from. So By following JFK’s head movement you can tell in which direction the shot came from, “back and to the left”. And who was back and to the left with gun that fires a frangible round, Hickey.