It is only by the grace of God that you've never heard my family mentioned in a deal like this. One reason I'm not quick to blame the family of the murderer in any way is because of some personal experience in this type of thing.
My brother, in his younger years, was always talking of killing people and breaking things in his rage. He didn't much care who he hurt, either. If he had ever gotten a gun you might very well have been reading of him slaying some person or another for no apparent reason, just that person was unlucky enough to cross his path. He did leave the house with a knife the last time he stormed out, but fortunately he cooled down before using it. Shortly after that he found himself in the nursing-home system where he has been since. A couple of years back he had a stroke and that has effectively pulled his fangs. The condition he's in now leaves him barely able to walk, much less hurt anybody.
As a family member, I have experience trying to talk with professionals who saw him over the years. They really don't listen, you know. It's a terrible thing to know your brother is like this, to try to talk to the professional who is going to let him out after only three days of care when he went in spouting rage and murder, and you know good and well that three days hasn't even scratched the surface. But what do I know? I'm only a relative, and the doctor has degrees from such and so university!
So--- a story like this comes up, and we blame the relatives who may have been as much a victim-- this time the perp killed his mother, too-- as anybody, unable to convince the powers-that-be that there is a serious problem. Until something like this happens.
A note: If someone talks of fishing a lot, buys books about fishing, loads up on fishing equipment and so on--- why would ANYBODY be surprised if the person brings home a stringerload of bluegills??? So it was with my brother--- his talk was consistently of murder and mayhem, he even got books and had a huge knife at one time, but if he ever carried out his threats the community would have been SHOCKED that a person who gave so much warning could actually do it. My advice: If someone is talking murder and mayhem, maybe someone should listen.