It seems that most of the debate and discussion I hear is about 1) whether the shooter's notes should be made public and 2) what was the nature, and origin, of the shooter's mental illness. While these are important questions, it is mostly the shared goal of prevention that makes them so.
Perhaps a more important question, currently under-discussed, is How did this person's warning signs go unnoticed and/or unreported by all those who were in contact with her in the months, weeks, and days before the incident?
Does such a disturbed person simply not arouse suspicion, or is there something in our society/community that hinders the reporting of it? Or hinders preventive intervention?
There could be many varieties of mental/behavioral pathology that lead to mass violence. We may not be able to cure mental illness, but the problem of recognizing and responding to red flags needs some serious investigation (regardless of one's views on red-flag laws). I hope someone is interviewing the shooter's contacts to gain insight into this.