The actions of the shooter make even less sense in the context of what The Daily Beast article has to say about the family. Short of some kind of mental illness, it hard to fathom how the young man came to believe killing people was a reasonable thing to do.
If this is correct, the perp comes from a family of medical and psychological professionals. If they couldn’t tell that he was a ticking time-bomb nut-job waiting to explode into mass murder, how could anyone identify the perp as a risk?