I think, but am not sure, a student can be escorted to the bathroom. Most lick-downs I've heard of, in the districts I work with, the school is locked down, but not individual classrooms, ie all entrances into the school are locked-down, but not anything within the school. The point is to keep anyone out who should not be there (hence keeping the kids in) and not to keep people stuck in rooms.......unless of course something is actually going on, ie Columbine, etc.
It is ridiculous to set a detective story in New York City. New York City is itself a detective story...
AGATHA CHRISTIE, Life magazine, May 14, 1956