Location: McWopetaz Metroplex, Illinois U. S. of A.
50 years ago - 1967 August 15 - Victor Hoffman slaughters James and Evelyn Peterson along with 7 of their 8 children in the couple's Saskatchewan home. One daughter, 4, hid under some blankets and was not noticed by the murderer. Hoffman was found to be not guilty by reason of insanity and sent to an institution where he died in 2004.
This my opinion and to the best of my knowledge, that is, if I'm not joking.