I have been following this baffling case, and trying to catch up since the beginning. What a head scratcher!
I tend to agree with those that believe that David himself drove the truck there, but why and under what potential influence or mental state I cannot imagine.
I am also in the smaller minority camp that believes that it is a strong possibility that David is in the vicinity of his truck, obviously not super close, but he just hasn't been found yet. I have followed far too many cases here to know how often, despite best efforts and highly experienced searchers, bodies can be and are missed.
My current theory is a mental state that caused David unease, anxiety, paranoia, perhaps heat or fever that caused him to want to escape the claustrophobic cab and get out, ditch the jacket, and possibly run, far farther than we think.
But in reality, I'm open to any possibility at this stage.
Also, it shouldn't matter when a human being is missing, but it makes me sad to think about all those poor little hungry baby piggies stuck on that truck for 12 hours, especially if they had just been taken from their mom's, probably to move them to the other farm. Pigs are really smart, as smart as dogs, I think, and I can only imagine a truck full of puppies in the same situation.
All that said, my sympathy for pigs sadly isn't enough to stop me from eating bacon anytime soon!