How did a kid who had previously written about killing people and been committed for a mental health exam legally acquire guns?

1- probably wasn’t legal. It’s easier to acquire a gun illegally than legally. 2- they stole it from someone who acquired it legally when no one was watching.

Why is gun violence in gang areas many times higher than other neighborhoods?

Uuuhh because of GANGS? Criminal organizations that dispute for territory, the right to sell illegal guns and drugs and the right to steal and rob in those neighborhoods.

Don’t mistake mass shootings in schools with gun fights in neighborhoods with high concentration of gang members. Those are just different.