There was a study done by the FBI a few years ago. No matter what the extenuating circumstances (IQ, mental issues, drugs) they could track the shooting back to a single triggering event.
We rarely hear what that event is, because the focus is always on the guns. They don’t announce it because it is usually not really defined for a week or so after the event. They don’t announce it because no one wants to know that little Brad or Buffy treated Malcom the Shooter like crap for months or years before he put a bullet in their head.
No, understanding the trigger event does not excuse the killer. But it explains the process and it could work to help prevent other shootings that will happen down the road.
‘Single triggering event’ is most likely the father leaving the home.