Couple an increase in mental health issues, with a decrease (near absence) of involuntary hospitalizations and treatments over the years as a piece to the puzzle ... it's no wonder more of these shooters are found to be psychotic.
Obviously there have always been people with mental health issues, but back in the early 20th century (for example), kids used to bring their rifles to school for gun club. They didn't go around shooting people. Not coincidentally, involuntary hospitalizations for mental illness was practiced.
