It started with a string of inexplicable occurrences: footprints in the snow coming from the woods to the back door, but not leading back; creaking in the attic; an unfamiliar newspaper in the kitchen. Then house keys went missing, and someone tried to break the lock on the tool shed.

Andreas Gruber, a farmer living 60 miles north of Munich, Germany, couldn't decide what to make of it.

He confided these strange incidents to neighbors and friends, but they were still stunned when, on a chilly night in 1922, Andreas and his family – wife Cazilia, daughter Viktoria, grandchildren Cazilia and Josef, and housemaid Maria Baumgartner – were slaughtered with a pickaxe in their home, the Hinterkaifeck ranch.

The bodies were discovered the following Tuesday, after young Cäzilia failed to show up for school. While police suspected robbery, they soon abandoned the theory after finding money in the house. Numerous interrogations turned up nothing. Meanwhile, autopsies revealed young Cäzilia survived her initial attack. While lying next to her dead family in the barn, she had torn out tufts of hair before finally succumbing to her wounds.

Creepier still? The killer stuck around. food had clearly been eaten from the kitchen; someone continued to feed the cattle. Neighbors reported smoke rising from the chimney and even the dog had been let out. Whoever slaughtered the residents of Hinterkaifeck stayed through the weekend and took care of the place before moving on.

More than 100 suspects were questioned about the killings – the most recent being in 1986. In 2007, students of the Fürstenfeldbruck police academy determined that the Hinterkaifeck murders would likely remain unsolved forever.

The Hinterkaifeck murders shook the public – both from the brutality and the bizarre circumstances surrounding the homicides.

Police deduced that Andreas, Cäzilia, Viktoria, and young Cäzilia were somehow lured to the livestock barn and slaughtered one by one. Afterward, the killer (or killers) entered the house and bludgeoned little Josef while he slept in his parents' bedroom. Then they headed to Maria's room and murdered her, too.