Episode Details

A group of teenagers are massacred in a nature reserve in 1973. Five people are attacked, four are murdered and one is raped. The crime scene was so gruesome and large that eight law enforcement agencies would need to get involved. They would discover that the events that took place that night were worse than they could have ever imagined. 

Sources:
Gitchie Girl: The Survivor's Inside Story of the Mass Murders that Shocked the Heartland: Phil Hamman, Sandy Hamman

Gitchie Girl Uncovered: The True Story of a Night of Mass ...
Book by Phil Hamman and Sandy Hamman