Notice I didn't come down against the school.
The bag very well could have contained anything.
However, once the kid was found to have made a joke he should have had a good butt kicking and let go.
Oh! thats right you can't spank a child so we have to tie up our police to do what teachers used to do.
Glad I'm no longer in school, probably would be sitting in some jail with most of my class, for one of the many silly tricks pulled on the other students.
Just remember that if you teach children that they have no rights, nor freedoms, they intern will not consider you to have any rights or freedoms as well.