Bomb Threat

Yes the title is right.  A bomb threat.  Here in Japan, the safest country in the world.  A bomb threat at the junior high school that Christopher attends!!
Yesterday morning at 11 o'clock Christopher came home from school.  Very strange.  The school is practicing for the annual field day, so the kids have 6 lessons a day which means finishing at 4 o'clock and then most days they are a bit late.  Coming back at 11am is unheard off.  I asked why he was home so early. Christopher said that a note had been found in the school entrance saying that there was a bomb in the school.  All the students were sent to the gym where they were told to go straight home while the police searched the school.  Christopher said that there was yellow crime scene tape across the school entrance and at least 20 police officers.  I just can't get my mind around the idea of bombing a junior high school, there is no reason that I can think of.  This is a small city, a nice place to live but not important enough to get the attention of terrorists, especially not the school.  So why a bomb threat?   The one thing I can think of is a kid not wanting to do the sports day practice, but would kids think of such a thing?   A lot of questions, I hope that Christopher has some answers when he gets back tonight!!!