The Gruber family and their maid Maria were mysteriously killed in 1922. This cold case feels like a ghost story, so get ready to get spooked. Sources: https://www.mentalfloss.com/article/502044/chilling-story-hinterkaifeck-killings-germanys-most-famous-unsolved-crime. https://filmdaily.co/obsessions/true-crime/hinterkaifeck-farm-murders/. https://en.wikipedia.org/wiki/Hinterkaifeck_murders.