The 1927 Bath School Disaster

The Bath School disaster is the name given to three bombings in Bath Township, Michigan, on May 18, 1927, which killed 38 elementary school children, two teachers, and four other adults; at least 58 people were injured. The perpetrator first killed his wife, and committed suicide with his last explosion. Most of the victims were children in the second to sixth grades (7–14 years of age[1]) attending the Bath Consolidated School. Their deaths constitute the deadliest mass murder in a school in United States history.[2]
The bomber was the school board treasurer Andrew Kehoe, age 55, who was angry after being defeated in the spring 1926 election for township clerk. He was thought to have planned his "murderous revenge" after that public defeat; he had a reputation for difficulty on the school board and in personal dealings. For much of the next year, a neighbor noticed Kehoe had stopped working on his farm and thought he might be planning suicide. During that period, Kehoe carried out steps in his plan to destroy the school and his farm by purchasing and hiding explosives.
Kehoe's wife was ill with tuberculosis and he had stopped making mortgage payments; he was under pressure for foreclosure. Some time between May 16 and the morning of May 18, 1927, Kehoe murdered his wife by hitting her on the head. On the morning of May 18 about 8:45, he exploded incendiary devices in his house and farm buildings, setting them on fire and destroying them.
Rest of story:
http://en.wikipedia.org/wiki/Bath_School_disaster