I study a lot about psychology and human behavior. I think it is very interesting to note that many of the past Serial Killers ( many involved shootings) were not related to any type of mental health issues.
That's just a fact. Most of them were related to Sociopathy and Psychopathy which are NOT mental illnesses. I repeat they are NOT mental illness.
I suspect a number of these Mass Shootings murderers involved much of the same dilemma as past Serial Killers. And they were not mental health issues like Schizophrenia, OCD, paranoia delusional, depression, etc..et..
Just bad seeds that deserved to be exterminated before all the mayhem they caused. imho