Bullying got worse due to zero tolerance policies that schools now have.

Used to be, if a bully pushed too far, they got punched in the mouth. Now, bullies get free reign with zero consequences. Even if another kid tries to teach them some respect, it's the kid that fights back that gets disciplined. The bully gets off scott free and is even more emboldened.

And the inability to fight back against bullies makes the anger fester and build inside the bully's target.

That said, it's doesn't make bullies legally culpable when some kid goes off and murders others. Kids get bullied ALL the time and don't murder people. It just means we have a systematic problem that allows bullying bullshit to continue.