Many things about the official story do not add up.

The weapon found doesn't make sense. It doesn't really look like an older imported Mauser. It could be a sporterized antique Mauser in a modern polymer stock. It could also be a modern Mauser brand hunting rifle. Which sort of contradicts "older imported" and "grandfather's rifle" descriptors. The scope is seemingly set back too far for prone shooting.

I have read or heard several claims he was shot from behind. I could buy that as plausible. Based on what I have observed with my own eyes. I think it is one of two possibilities.

The only thing I am suggesting is that it's not impossible for a frangible bullet to deflect, ricochet, and fragment from it's path from hitting spinal bones.

It could be the bleeding from his neck was caused by entry and he was shot from the front. It could be bullet hit spine, fragmented, ricocheted and we're seeing small fragment exit neck having been shot from rear. If he was shot from the rear was there another object in the path that absorbed some energy, maybe?

There is a hole in his neck where a projectile, or fragment, either entered or exited.

It's not impossible for spine to deflect or fragment, preventing a bullet from exiting. Nobody has made public the type of bullet used in the shooting. Different bullets can be designed to do things such penetrate, expand, or fragment. Something can be implausible or unlikely, but not impossible.

Again you're proclaiming something you're largely ignorant of the skeletal structure and body composition of a deer compared to a human. It's not a horse sized animal. A large mature buck weighs over 200 lbs, about the same mass as full grown man. I have an 18" neck. Some deer might have a 15" neck, larger may have 22" neck. Deer do have larger chest cavities than humans. But they don't possess any special properties that change terminal ballistic performance.