That is fake. Leavelle did not have his arm there. But, why did they fake it? It's because of this photo.
So, that must be fake too.
That's an unnatural line there. You can see where his shoulder is and his arm coming down from his shoulder. They stuck that extra appendage in. Why? It may have been just to cover up the area so well that nobody could complain about the lack of disruption of the clothes and the lack of blood. Look how totally obscured the area of the gunshot is: it is completely and totally covered up.