Guns saved lives.
In the Columbine shooting, if there were no guns, the bombs and chemical weapons, they would have spent more time on those, and probably killed half of the school. Instead they focussed on the guns harming/killing one person at a time.

Just had to throw this tidbit in.

Unfortunately, your three warning signs are just one sign.
An inability to work out pent up rage, almost always from an abusive childhood position they couldn't get out of. Almost always from a single mother.

The problem is, many of these people grow up and heal themselves.
Many get out from under the single mother abuser, and go out to be very empathic and caring people.
And a few, take out their frustration on their schools.

I strongly suggest we abolish govern-cement schools... i mean, low security prison indoctrination systems.