Creative Speculation

As I've said a couple of times now, the first frame in my animated gif is before the hit and the second frame is clearly after the hit. No, it does not "represent the impact"; it's our best available evidence of what happened immediately after the impact. There is no ambiguity in what that second frame shows -- a forward head snap -- and there's no mystery about why it happened: The bullet imparted forward momentum to the head when it passed through from rear to front. Momentum transfer is instantaneous; it's completely impossible for it to have the delayed action you're suggesting two frames later. This is "basic science" and I'm not interested in any imaginary science you conjure up to try to protect your conspiracy delusions.

I'm pretty sure you already know that there are several possible explanations for the "back and to the left" movement two frames later, but there is no reason to discuss them here. The truth that you suddenly seem to be very afraid of is that that motion can't possibly be because of momentum from the bullet, which is long gone from the scene by then, so that motion can't possibly tell you where the bullet came from. The immediate forward head-snap, on the other hand, certainly does, because there is no other reasonable explanation for it except momentum from the bullet.

I'm sure it's very frightening to be confronted with the fact that you were so wrong about something you were so sure about for so long, but reality can be like that sometimes. You need to inspect the evidence more carefully, and I dare say that advice applies to a great many of your beliefs.