The police report was redacted but it appears the grandmother was on 2-3 medications with side effects. Whatever condition she was taking them for is redacted. One week after the incident the deputy asked the grandparents to come to the office for a formal interview— she said she wanted to put away her Christmas decorations first??!! Very strange, IMO.
The report also suggests that Tracy stated she had already fallen asleep with the little boy and the garage door had been left ajar before the grandfather left. Over his statement that she had been awake and he'd put a weight behind the door when he popped out.
Though police obviously decided she was the one who was culpible.
There has been more to this. Was she fit to have charge of a child? Did her mental health, medication regime or cognitive state make her fit as a caretaker? Did she get assessed after the first time? Were there any red flags in her quality of care between these two incidents?
It is possible for two terrible accidents to happen without a significant pattern of negligence. The odds are long, but the universe will roll those dice somewhere terrible as the idea is (and as little as people want to believe it.) I think a lot of investigation into her pattern of care will be needed.
I wonder if she does show a pattern of dangerous negligence or absent mindedness that the parents were aware of, if they will also catch some culpability. Grandparents and parents may differ in childrearing occasionally, but after one child's death, I would expect parents (if they could ever bring themselves to allow grandma to watch their kid again) to take a zero tolerance approach to any lapses.