The police are not social services or psychiatrist - and even if they had some experience, seems like they did their part - just my opinion from what I have read or seen. I wonder if the parents had any ideas of how the relationship was and if they did, I bet they would not have been able to encourage them not to be together. They have to blame someone. Perhaps they could not get any money from Brian's parents.
So many children/women, have died from neglect/abuse. Is every social worker and teacher going to get sued for missing signs, not doing enough.......
Just thinking out loud. Very sad all around and hard for any parent to live with. Having said that, who knows what I would do if I were in their shoes.