Gosh, this is a tough one. I'm not a fan of those surveillance cameras, especially in public places, but I also don't think folks have the right to disrupt the lives of others with bomb threats. It's illegal to falsely cry "Fire!" in a theater, and this is worse, since it's being repeated.
I'd suggest the school goes CSI (Crime Scene Investigating), find the culprits, and let them know this shit is not acceptable, or funny.