Thomas Hamilton shot dead 16 children and a teacher in Dunblane, then himself.
Killing rages such as those experienced with the Dunblane tragedy (or Colombine, the recent German School massacre etc.) nearly always end with the murderer killing themselves. It is not exactly understood why, but it may be associated with high testosterone levels (which controls violence) and low levels of seratonin (which is a key componant of the self control mechanism, and affects self image and happiness).