You missed the part that says "viewed and listened to hours of video from the bus". The evidence is already available. The problem is that no one was bothering to look at it to check the kids were OK.

Kids will find ways to harass each other: between classes, lunch times, recess, etc.

This is true, but in most countries it doesn't escalate to mass murder. That's specifically a US thing (https://worldpopulationreview.com/country-rankings/school-sh...). So while you're right, I don't think it's fair to suggest it's hard to stop this problem or to resign to it being typical kids behaviour. The shooting aspect bucks the global norm.