In his book "Best Evidence", David Lifton says that the wounds on JFK were all altered to make them appear as if the shooters were located behind him. In reality, Lifton says, all of the shooters of JFK were situated in front of him. No one, he says, fired a shot from behind JFK.
These alterations included creating "two false entry wounds" to the rear of JFK's body, one to the back of the head and another to his upper back. Both were done, again, to make it appear that JFK was shot from behind.
Additionally, the alterations also included enlarging the neck wound and the head wound on the right side of JFK's head to make them appear to be exit wounds.
Again, this is all explicitly stated in his book.