Depression and suicidal thoughts in teens are extremely common. I suspect depression at its very basic affects more than it doesn’t during the teen years. We can’t use those to figure out who is dangerous TBH. When we talk about mental illnesses we’re talking about things like psychopaths or delusional folks - more common beliefs about who can kill vs the belief that a “regular” person could never do that. They often aren’t loners either.
In reality, just as with the VB shooter, he can be the man working next to you who just brushed his teeth.
That said, we try to help those with depression too. We just don’t assume they are going to kill others.
Since it’s impossible to predict who’s going to snap and nearly impossible to do much just seeing signs, it’s very important to teach coping mechanisms because absolutely all of us are going to have something go wrong in our lives at some point - and pretty much anyone can access a gun in this country.
It certainly won’t be 10-12 months before another one happens somewhere. Unfortunately, they are far more common than that at this point in time.