It's not just a failure of the schools to report actionable crimes to the police, or the police to take action on a clear pattern of antisocial behavior, or mental health workers to take action on clear mental health issues, or of the police to actually go inside (there is some indication a stand-down order may have been issued), or the FBI to take action on clear tips.
No, it appears that the murderer's mom didn't even know who his father was, or the father of the murderer's brother. In other words, the birth mother was quite a loose lady, and we would then ask a followup question; were alcohol or drugs involved? Former adopted children of my brother-in-law and his wife did suffer from fetal alcohol syndrome, leading to great difficulties and their eventual un-adoption (and adoption by another family better equipped to care for them).
Which leads to another thought. If we assume that none of the murderer's actions prior to the Parkland murders were criminal--debatable, but let's go with it--we then might ask whether a pattern of antisocial, but not yet criminal, behavior ought to trigger further investigation and intervention in a young person's (or adult's for that matter) life. It would function, really, along the same lines as the biological passport that led to Lance Armstrong being banned from cycling for life.
And at best, this would be assistance, not prosecution. My brother-in-law's experience was that presumably well-meaning social workers seemed very eager to lower the boom on him and his wife, but were not willing or able to partner with them and help them. And of course, the kids paid the price for that. We might do well to consider a paradigm shift in social work.
Update: if the Department of Justice is compelling schools to handle things in house instead of reporting them to the police, isn't that a clear violation of state mandatory reporting laws? Would we not then go after the law licenses of the DOJ lawyers involved? I think the clear answer is "yes, I sure would do that."