One day in March 1922, German farmer Andreas Gruber told two neighbors of a curious discovery. He had found traces in the snow leading from the forest to his farm, but none leading back. He’d also found a strange newspaper. The neighbors dismissed his story, and Gruber didn’t contact the police.

Four days later, when Gruber’s granddaughter failed to appear at school, some neighbors trekked to his farm. There they found six mutilated corpses: Gruber’s entire family and a female farmhand had been murdered with a pickaxe. An autopsy showed that the 7-year-old granddaughter had been badly injured in the attack but survived for several hours. She had lain in the straw amid the bodies of her family, pulling out her hair in tufts as she died.

That’s the whole story. Police have interviewed more than 100 suspects, one as recently as 1986, but to this day no one knows who killed Andreas Gruber’s family or why.