On May 18th, 1927 Andrew Philip Kehoea, a disgruntled school board treasurer,, bombed the Bath Consolidated School in Bath Michigan killing 36 schoolchildren and two teachers. As rescuers began working at the school, Kehoe drove up, stopped, and used a rifle to detonate dynamite inside his shrapnel-filled truck, killing himself, the school superintendent, and several others nearby,

http://www.slate.com/blogs/crime/2012/12/18/bath_school_bombing_remembering_the_deadliest_school_massacre_in_american.html