This happened a couple years ago. The note was found in the bathroom, the principal read it, crumpled it up and said what note. He thought it wasn't credible and did the right thing. My wife thought it was horrible that he did that.
Currently the same thing happened to a local district, police were called, building was placed in lockdown. A big deal was made about it. Within a week, two more incidences happened.
It is silly over reaction making things worse. They should have thrown the first note away.