Across the board. I do agree there are people who should be separated from society for their whole lives, but fun fact: School shooters are not one of them. You may not agree with this because I'm assuming you're American and the word prison for you means "retribution" rather than rehabilitation. But a functioning mental health system actually does allow people who have committed a crime to reintegrate into society. It's what countries with actually reasonable incarceration rates, and far lower rates of recivedism than the USA do.
You picked a very low hanging fruit there. School shooters are almost universally troubled young and still malleable minds and more easily rehabilitated than many other class of criminal. On top of that, the real question is, why focus on school shooters at all instead of the system that has so utterly failed to the point where they exist. Ask yourself why they are almost uniquely American.