Keep in mind, that from Columbine HS on, running out of your favorite flavor of mental meds can be a killer deal.
There are lots of questions here about mental health history, medication, etc. The guy had served in the Marines and had a purple heart. What conditions surrounded that, and his disposition when he got back.
And to really reach, did someone send a bad batch of meds to troubled retired Marines? The church shooter in MI was said to have served as a Marine, also, to be the same age (40), and served in the Iraq war.
One is an incident, two starts a pattern.
(Gibbs rule 39 applies)