From Texas Standard:
On Sept. 15, 1959, an ex-convict new to Houston attempted to enroll his 7-year-old son at Poe Elementary, near Rice University. School officials denied his enrollment, saying he lacked the proper paperwork. The man later returned to the schoolyard with a briefcase and some obscure messages. He then exploded the briefcase, killing himself, his son, the school's custodian, a teacher and two young students.