Everyone thinks this is a "new" deal but this has happened, unfortunately, before.
Andrew Kehoe was mad that he was losing his farm in Bath Township, Michigan, because of school taxes. So, for about a year, he used his job at the school, which gave him access, to fill the school with hundreds of pounds of pyrotol.
On May 18, 1927, he killed his wife and burned down his farm. While firefighters were at the farm, a bomb went off at the school. 38 kids (2nd to 7th grade), 4 adults and two teachers were killed.
The bomber then detonated a car bomb filled with fragmentation devices, as rescuers arrived. The superintendent and Kehoe were both killed by the car bomb. Bath School Disaster