The Pathway To Violence.

The .. 'etymology' of "Mass Shooters" is bizarre, frightening, But perhaps not beyond understanding.

 One author attempts to explore the phenomenon.  Whether he is successful is subject to your interpretation.

But one thing is clear ... if anyone offers a way to predict mass murderers, it bears closer examination.

Everything We Think We Know About Mass Shooters Is Wrong - Esquire:
By Tom Junod on September 16, 2014

Mass shootings are not unstoppable, and there are people trying to stop them. They are not even inexplicable, because every time Trunk hears of one he understands why it happened and who did it. We have come to believe that mass shooters can't be stopped because we never know who they are until they make themselves known. But Trunk was almost one of them once. He was a heartbeat away. And what he understands is that shooters want to be known, not through the infamy of a massacre, but before they have to go through with it. They want to be known as much as he, years later, wants to remain unknown, walking to the bus stop in the rain.