Kennedy didn’t kill himself...
There was always a second shooter or primary shooter who lopped off the right side of Kennedy’s head, driving the skull backward with the trajectory of the bullet
Oswald didn’t do this.
There are problems with that theory.
Where are the bullets, bullet fragments, bullet holes, or wounded people behind Kennedy? There are none. There are bullets/fragments and wounded people in front of him.
Rifle bullets -- I won't say always, but almost always -- leave a ragged, nasty exit wound and a small entry wound. Almost any hunter knows this from experience. Kennedy's ragged, nasty exit wound was toward the front.
Kennedy's head snapping backwards just means that the bullet imparted little momentum entering the skull. Exiting the skull, it and exiting tissue fragments imparted lots of momentum by Newton's third law.