For me, the most surprising takeaway was how many shooters exhibit signs of trouble prior to the shooting and how difficult it is for teachers and law enforcement to do something about it.
Clicking around one thing that stands out to me is a striking increase in assault rifle usage https://www.theviolenceproject.org/data-on-social-media/prev...
The Violence Project makes the argument that it’s not just mental health and availability of firearms that causes mass shootings. It’s a confluence of many contributing factors that all need to be addressed.
This is why I found the book so enlightening given the typical mental health and gun control debate that is going on now. This is not a simple problem to solve in my opinion.