Shouldn't there have been more investigation into the father who was the 'main suspect' in this case?

After the mother's death, the husband and father of two children, kept after the courts to give him custody of them. He was awarded supervised visits. The man who was father to two young children, killed their mother while they were all together on a camping trip. They remembered what the father had done and when they got older, they told people what they had witnessed. They stated, "Mom was there with us, then she was in the trunk, and after that she disappeared." After the social worker came with the children, the father closed the door in her face instead of letting her accompany them for their visit. The social worker said she smelled the prevailing smell of 'gas.' Then the house exploded, which resulted in the murder of the two children and himself.