True stories to base our narrative on

1969: Film star stabbed in 'ritualistic' killings

Sharon Tate 26 was a wife of a film director and her along with her friends were violently killed in a home invasion attack. Sharon Tate who was eight and half months pregnant at the time, and her five friends were brutality attacked, shot and stabbed in her Los Angeles home. The police reported that the attacked looked to be a 'ritualistic' killing, there was blood smeared all over the walls, and words written in blood around the premisses of the home, and the phone lies had been cut. The person who was believed to be behind this was Charles Manson who ordered his cult follows to do this horrific crime. 
Many horror movies that I have looked at our based on odour loosely based on true events, this is represented in one of my previous posts, and we might consider using a real life event as a basis for our narrative.