Ok, everyone put their sleuth hats on (tin foil are allowed too).
I think the majority of people are thinking accidental death is most likely, as opposed to premeditated murder.
What we have to figure out is, WHO benefits most from a cover up? Who had/has the most to lose?
Theory 1, VDK could lose his commercial driving license and therefore his employment. I'm not sure, but he's not still doing that job anyway, is he? So that doesn't make sense, why would he cover up the death of his son just to save a job he doesn't keep anyway?
Theory 2 I've seen, JM is scared she'll lose her other two kids if she's responsible for the death. I don't buy this for a couple of reasons, first of which is that she really didn't seem to care much about having those kids in her life anyway. She voluntarily gave them up to their father, and she didn't see them very often anyway. Second, if it was really an accidental death, she wouldn't lose visitation rights with the other kids anyway. Lots of parents have accidentally caused the death of a child and don't lose their other children.
I blindly accepted from the beginning that Great Grandpa was elderly, oxygen dependent, and unable to even care for himself without daily assistance, because it was reported in the beginning that JM was his "caregiver".
Looking back, there are reasons to doubt this. He's definitely elderly and oxygen dependent, but he's on a low enough oxygen supplement that he can use the small portable tanks. This means he's probably on 3 liters or less, because once you get above that those tanks empty fast. He probably has a concentrator at home, but he would have needed portable tanks for camping and fishing, because there was no electricity at that campground. Do campers like his have generators that could support the electricity draw of an oxygen concentrator all day?
Plus, he was able minded enough to drive himself and Isaac there in his Suburban, pulling the camper, on mountain roads, at least partially after sunset if they did arrive Thursday night. Now, a man with memory issues could still be capable of this, but it's still something to consider.
LE didn't name him for weeks after the investigation started, and they immediately said he had health issues and essentially implied he couldn't have had anything to do with the disappearance due to these issues.
Yet, we're supposed to believe VDK and JM thought him capable enough to supervise D only a few yards away from a steep embankment that had a creek at the bottom. Would they have really left a 2 year old who was a "mover and a go-er" in the words of his father in the care of a man who was so unhealthy he couldn't possibly have anything to do with the disappearance?
I'm wondering if Great Grandpa is the one being protected here, by both family and LE. But if he is, WHY? What consequence could there be to him that would make covering up the death of a little boy worth it? Does he have money?
I think if we can figure out who benefits the most from covering up the accidental death, we can figure out what really happened.