One of my early thoughts were of little Sherin Mathews whose parents weren't able to "accept" her because of her physical challenges. Remember how there were no pictures of her (Sherin) in their house?
Nothing made sense in Thaddeus' disappearance and the lack of the parents publicly appearing to plead for him just darkened the cloud. And of course hearing from LE that the parents stopped cooperating almost immediately sealed the deal.
IMO it's one thing to be overwhelmed by caring for a special needs child and quite another to choose to murder and burn that child. And I know you feel the same so I admire that you are able to look at the facts from all sides. I feel like I get more and more jaded with each case that ends with caretakers "solving" their problems with violence.