After reading the entire report, I disagree. I think the cops at least thought there was something else going on, but didn't have enough evidence. JMO
The disconnect I have is that the nanny stayed with the family after she killed the grandmother. I don't think it matters whether it was an accident. The nanny was obviously very careless around family members and could be a risk to the children. Furthermore, she would also be a constant reminder of the loss. The normal thing would be to immediately replace her. That didn't happen, so the question is why.