I love reading about unsolved mysteries, especially weird/creepy ones, and the Hinterkaifeck murders is one of most fascinating to me.
A farmer in Germany back in the 1920s had noticed mysterious footprints in the snow around his house. There was also strange stuff happening around the farm. Footsteps in the attic, a newspaper that no one in the family had bought, and eventually the house keys disappeared. What makes it stranger is that the housekeeper had left a few months prior, swearing up and down that the farm was haunted.
The family suddenly went unseen for a couple of days. Their neighbors went to check on them, only to find the entire family as well as their newly hired housekeeper had been murdered. Most of the family had been lead into the barn one by one and slaughtered with what’s believed to have been a pickaxe. The maid and their youngest son were killed in their beds. The worst part is that the youngest daughter lived for a few hours after the attack. She spent the last few hours of her life lying next to her dead family in the hay of the barn, and had torn chunks of her own hair out in that time.