BBM, Outrageous criminal acts are not reasonable.
I do not see this grandmother & grandfather, living out their golden years, rather quietly & graciously, doing anything to anger someone so much to cause murderous rage. All I have read, points to their being respected & living in harmony with family & neighbors.... But my thoughts are based on legal, moral, ethical & socially-acceptable actions.
Also, I balk at the idea of retaliation for long-ago business deal that went bad. Hasn't Mr D been out of the corporate world for many years? On the other hand, someone who would attack, kill & dismember doesn't think the way I think.
All along, I have expected the perp to be a nutcase in the neighborhood who went off the deep end or a wholly random person(s), thrill kill type thing. When Sheriff Sills makes the announcement of arrest(s), I think we will all be thinking "Why? This makes zero sense."
One would have expected robbery to be part of this horrific crime. Minus that, we are looking everywhere. Of course the investigation must check family, neighbors, other associations, business dealings, even the infamous Eatonton cult connection. I think sometimes we over-think possibilities & come up with a script for a really bad tv movie.