Honestly I would argue we need to expand our definition of what a mental illness is, in order to help these folks get treatment before they go and shoot a bunch of people.

With that being said I think it's important to call out this distinction for two major reasons. For one, it shines a light on the fact that someone having any mental illness does not mean they are going to go on a mass shooting. For two, it also shines a light on the fact that the people who do break in this way aren't understood well - if they don't classify neatly into the existing mental illnesses we have, we by definition do not have good research on the subject. Do patterns exist among this population of mass shooters that we can identify? Are there specific ways that they think which are maladjusted and can be corrected through existing education and mental health offerings? Might they belong to a larger group of illness which also includes other folks who are suffering in other ways, where studying this group might shed light on other folks who need help?