This actually is based on true events! The writer and director from the first movie, Bryan Bertino had an experience when he was younger when a stranger came to his house asking if a person who didn't live there was home. Later on, he discovered that the person knocking was responsible for multiple home invasions in the neighbourhood.
Fun fact! the stabbing scene was actually used with a cardboard box and the person stabbing the mother was the person playing the mother! yes thats right, the mother was the cause of her own death.
This film is based on true events such as the writer, Bryan Bertino's own experiences.