In March 1922, Andreas Gruber’s farm was the setting of some strange—and altogether creepy—occurrences. From a forest at the edge of his property, Gruber had discovered a set of footprints leading to his farm…but no set of footprints leading back. He had heard footsteps in his attic, Gruber told his neighbors, and had also found a newspaper that didn’t belong to anyone in his family. His house keys had even gone missing. Many people in Gruber’s situation would have contacted the authorities, or at the very least sat up nights with a shotgun in hand, waiting for an intruder to appear. However, Gruber must not have been overly concerned; he neither reported the happenings to the police nor moved his family away from the farm where the threat of ominous activity seemed to grow every day.

That lack of action cost Andreas Gruber dearly. By the beginning of April, he was dead, as was every member of his household.

In what has become known as the “Hinterkaifeck murders,” named after the southeastern German farmstead where Gruber and his family met their end, six people—Andreas; his wife, Cäzilia; their widowed daughter Viktoria; their grandchildren, 7-year-old Cäzilia and 2-year-old Josef (who were Viktoria’s children); and the family’s maid, Maria Baumgartner—were brutally slaughtered by an assailant who remains unknown to this day. Though more than 100 suspects have been considered, German police academy students who re-examined the case in 2007 determined that with the passage of time, not to mention the archaic investigatory practices that produced the evidence with which modern-day authorities must work, there is no chance that the murders will ever be definitively solved.

Neighbors who paid a visit to Hinterkaifeck on Tuesday, April 4, 1922, several days after the farm’s inhabitants had last been seen, likely had no idea that they would be encountering the scene of a crime that would occupy the minds of both police and armchair investigators for decades to come. The search party had been drawn to the farm because young Cäzilia had missed school the previous Saturday, while the entire family hadn’t shown up for church on Sunday—incidents unusual enough to merit a visit from concerned townsfolk. The reason for these absences became apparent when the bodies of Andreas, his wife, his daughter, and his granddaughter were found in the barn, their heads destroyed by what investigators would later determine was a mattock, a tool similar to a pickaxe. In the house, neighbors discovered the bodies of Josef and Maria, who had fallen victim to the same method of attack. Investigators were called to the scene and pinned the date of the deaths as Friday, March 31. This determination was especially eerie because neighbors had reported seeing smoke coming from the Grubers’ chimney throughout the weekend—an indication that the murderer had remained on the property for at least a few days following the crime. This belief was supported by the fact that the farm’s animals had been fed, the family’s food had been eaten, and a bed had been slept in, all while the bodies of the Grubers began the slow process of decay.

The destruction of Hinterkaifeck’s residents was a conspicuous end to a family that already had a specter of scandal surrounding it. The Grubers, at least some of them, were not well-liked by members of their community. Andreas was said to be a recluse who beat his wife and children (and, if rumors were to be believed, who had engaged in an incestuous relationship with Viktoria that had resulted in the birth of Josef). In addition, six months before the murders, the Grubers’ previous maid had left the farm in a hurry, claiming that she heard strange voices and footsteps and insisting that the house was haunted. The new maid, Maria Baumgartner, started her job on March 31—the last day of her life.

The police immediately set about in search of a motive, which, they hoped, would lead to a suspect. Robbery was ruled out; although the Grubers were well-off, none of their valuables had been touched. Maybe the motive was revenge. Viktoria had claimed that a local man named Lorenz Schlittenbauer was Josef’s father; at the time of her murder she was planning to sue Schlittenbauer for financial support. Schlittenbauer was one of the neighbors who had discovered the carnage at Hinterkaifeck, and the men with him at the time noted that he seemed oddly unfazed upon finding the body of the woman he had once courted. Police investigated him, but ultimately didn’t find enough evidence to charge Schlittenbauer with the crime.

Another proposed suspect was Viktoria’s husband, Karl Gabriel. He had been declared dead while fighting in World War I, but his body was never found. According to one theory, Gabriel didn’t, in fact, die. Instead, he faked his death with the intention of starting a new life, then changed his mind. When he traveled to Hinterkaifeck and found his wife either engaged in an incestuous relationship with her father or having borne the child of Lorenz Schlittenbauer, Gabriel killed the entire family in a fit of rage. Admittedly, this theory strains credibility, for although Gabriel’s body was missing, several soldiers indicated that they had seen him die in a trench in France.

Not only have a suspect and motive remained elusive for nearly a century, the sequence of events that led to the deaths of the Grubers and their maid can’t be definitively established. With no survivors to describe what happened at Hinterkaifeck on March 31, 1922, any theory is merely conjecture. However, investigators believed that somehow the murderer was able to lure the four eldest Grubers to the barn, one by one, and then kill them. At that point, the murderer entered the house and killed Josef and Maria. Most of the Grubers were found wearing their nightclothes, so the murders probably occurred in the evening, under cover of darkness. The attacks were devastating enough that Andreas, the elder Cäzilia, and Viktoria died immediately, but the younger Cäzilia had apparently been alive for a few hours after the assaults; she was found with tufts of her own hair in her hands, likely pulled out in spasms of pain and despair.

The indignities heaped upon the Grubers didn’t end with their deaths. Their heads were sent to Munich for investigation, but were lost during World War II. Therefore, the six bodies buried in a graveyard in Waidhofen, the municipality in which Hinterkaifeck was located, are headless. One year after the crimes, the farm was demolished so that it would no longer serve as a grim reminder of the violence that had visited the community.

Although the students who investigated the murders in 2007 indicated that the case could never be solved, they did settle on the most likely suspect. However, out of respect for the individual’s descendants, his name was not made public. Thus, the possibility exists that the man who committed the Hinterkaifeck murders will in death—as he did in life—escape the earthly penalty of having his identity exposed as one of history’s most depraved murderers.