Horrors based on true events

Borderland is about three friends who go to mexico to celebrate their graduation, and along the way get involved in cults. The film is loosely based around Adolfo Constanzo, who was an American serial killer who was a cult leader. 

The girl next door is based on true events about two girls who are orphaned and sent to live with their aunt. However they are kept captive and subjected to torture, rape and severe beatings. The true story was about parents who left their daughter with a family friend whilst they worked in the circus. Sylvia Likens was tortured with similar events to the film, and it was only discovered once she died at the hands of this family friend. 

Two women and one man find themselves stranded in the outback when their car breaks down. In the film a truck driver kidnaps and tortures them, whereas in the true events hitch-hikers were kidnaps and tortured in the 90's by Ivan Milat. 

Texas chainsaw massacre is loosely base on the serial killer Ed Gein, who when he was arrested had in his possession nine human skin masks. And from the use of mise en scene in the film poster you can see that the character is wearing a skin mask as part of his costume. In the movie the antagonist captures and kills his victims and then he uses their skin. 

Many films I've seen whilst researching were loosely based of the serial killer called Ed Gein. These other films are 'Psycho', and  'Deranged'. So when considering a narrative we could use a story that has already happened and then develop upon that, to create our narrative. It is one idea that I would like to consider when thinking of what are narrative is going to be about. We could make an entirely different narrative, but basing it on something that has previously happened makes it even more terrifying. It doesn't have to be completely based upon a story, just loosely because the majority of the upon movies use it as an idea and then develop on that, they just use it as a guideline.