In this particular case I believe her stupidity in keeping unsecured guns in the house and teaching her son to shoot has already been discussed. She provided both knowledge and access and taught him to shoot. No access, and the shooting would never have occurred. If he hadn't been taught to shoot the shooting would never have occurred. I said earlier that I considered her at least as responsible as her son, but frankly I was trying to be civil and not speak too ill of the dead. My actual opinion is she is responsible for the shootings. He might have done some other evil deed - who knows, but with no access and no knowledge of firearms he could not have done what he did...
After dealing with the idiocy that calls itself MH in this country, it may be that she tried to take guns out of house or limit his access to them and shooting, but his doctor/therapist told he she was infringing on his rights.
I saw this working with group homes, things that made perfect, logical sense, were set aside by therapists, welfare or their guardians. Such as allowing the child molesters/violent "consumers" to watch wrestling, or taking them to learn martial arts. Frankly when you have people like that that are already violent and broke their mother's arm? They don't need to learn anything else that will enable them to hurt people. And if someone has molested a 4 year old? You don't give them access to porn either...but such is the state of mental health in our country that it thinks those things make sense.
And when he first learned to shoot guns, there may have been no cause to think this would happen.
And for all the push to lock doors, bar windows, and keep people like this out of schools, all he would have had to do was crash a car into building, or circle it with can of gas and torch it and what then?
The mentally ill in this country are being watched over by a band of lunatics for that matter. No common sense among any of them.