The Grassy Knoll
There was a second shooter, James Files, hiding behind the grassy knoll where Kennedy was shot.
The day after the assassination, a bit of bone was found where just after the car where Kennedy was shot. This shows that he could not have been killed from behind because the skull fragment could not have gone that direction.
Against the Theory
With these pictures being the only evidence, some people are saying now days that they have been altered from the original photo to make it look like something is there.