That's much like, The Texas Chainsaw Massacre - based on a true story. How Ed Gein killing two women, and digging up graves became a dude chopping up sexy college kids on a road trip: I'll never know.
I went to school in a prison town, and every once in a while I would hear some prison guard say that they met the killer from the Texas Chainsaw Massacre... Then I have to tell them that he never existed.