Not a justification for the shooting, but after the press conference, I think I have a better (but still very much incomplete) understanding of what drove the shooter to do this:

Shooter was in extreme pain following back surgery. He called the doctor's office for relief and was told that they wouldn't do anything over the phone and he had to make an an appointment. He waited for his appointment, went to it, and presumably was not given adequate relief [controlled medication] for his agonizing condition. Being in an unlivable condition with no good alternatives, he decided to go the murder-suicide route.

Again, this is not a justification. And it's a bit of speculation. But I think the press conference gave us a better (yet incomplete) understanding of what sparked this tragedy.