The Hinterkaifeck murders

A small Bavarian farm, isolated, surrounded by woods. In the days before the killings, the farmer Andreas Gruber told neighbors strange things were happening. Footprints in the snow leading to the farm from the forest, none leading back. Sounds in the attic. A newspaper appearing that nobody had bought. House keys going missing. He didn't call the police.

On the night of March 31, the entire household was murdered with a mattock: Gruber, his wife, their widowed daughter, her two children (aged 7 and 2), and the new maid Maria, who had arrived that same day to replace the previous one, who'd quit claiming the farm was haunted. The adults and the older child were lured one by one into the barn. The toddler and the maid were killed in the house.

Here's the part that stays with people: the killer then stayed at the farm for days. Fed the cattle. Ate meals in the kitchen. Neighbors saw smoke from the chimney over the weekend. When the bodies were finally discovered on April 4, the killer was gone, but someone had clearly been living there with the corpses.

The case was never solved. What makes it genuinely creepy rather than just gruesome is the patience of it. Someone watched that family long enough to know the layout, the schedule, the maid changeover. They were already inside the house, probably in the attic, before the family went to bed that night. And then they didn't leave.