By definition a school shooter is a threat.
For as long as they're school shooters, sure. You seem to think that this is some sort of life-long brand instead of a temporary designation.
You seem to think that people can't ever stop doing an action.
You also seem to have an over-reliance on labels.
A kid who brings a gun to school to kill the one bully that tormented them, are they a school shooter?
Does it mean that they're going to go on a spree and kill as many people as they can before finally turning the gun on themself?
Are all school shooters spree killers?
Must all school shooters never stop being school shooters until they are dead or captured?
Is it possible for a school shooter to flee, and have no intention on killing any more victims?
You're the one making all these assumptions about what a school shooter is, based on a label, just like in this scenario.