Not sure how much interest there will be in this topic, but I'll give it a go and see what comes of it.
I'm looking to start a thread devoted to discussing famous and perhaps not-so-famous unsolved mysteries. I'm inviting everyone here to not only post examples of mysteries that are particularly fascinating and/or chilling to them, but also provide any additional info, opinions, and theories that they may have regarding any cases that are discussed.
I'll try to get the ball rolling with a mystery that has always sent shivers down my spine: The Hinterkaifeck Murders
* in best Robert Stack voice *
Neighbors had begun to worry about the Gruber family.
Sure, smoke continued to billow from the chimney of their Bavarian farmhouse, but the family members themselves had not been seen or heard from in a few days.
And so, on April 4, 1922, the concerned neighbors headed out to the Grubers' farm located about 1 kilometer north of the hamlet of Kaifeck (hence the name "Hinterkaifeck," or "behind Kaifeck"). What they discovered upon arriving there would surely haunt them for the rest of their days.
Inside the Grubers' barn lay the bodies of the family patriarch, Andreas, his wife Cäzilia, their widowed daughter Viktoria, and Viktoria's daughter, also named Cäzilia. All of them had been bludgeoned to death with a mattock- or pickaxe-type tool and then covered with hay. Inside the farmhouse, the neighbors found two more bodies - those of Viktoria's son Josef and the Grubers' new maid, Maria Baumgartner.
Police estimated that the murders had occurred on the evening of March 31. The victims in the barn were believed to have been lured to their deaths one at a time, after which the killer(s) entered the house and slew the remaining two victims. The younger Cäzilia had apparently remained alive for some time after being attacked, as police found that she had torn out tufts of her own hair. But perhaps the most chilling aspect of this crime may be that the killer(s) continued to live in the house for some days after the murders, going about his/her/their daily routine like dining in the Grubers' kitchen and even feeding the farm animals
(hence also the smoke seen rising from the chimney).
As police investigated the horrific crime, even more chilling details began to emerge about the Grubers' final days. Neighbors reported that Andreas had complained to them about a number of unusual incidents that occurred on his farm in the days preceding the murders. A mysterious set of footprints was found in the snow, leading from the outskirts of the property toward the farmhouse, but not
back out again. An unfamiliar newspaper was found on the property that did not belong to any of the family members. A sound resembling footsteps could be heard emanating from the attic at night, but Andreas could not find any indication of anyone being in there when he searched. One of the house keys went missing, a padlock on a shed was found broken, and one of the farm cattle was untied. None of these incidents had been reported to the police, however.
In a twist of tragic irony, the maid Maria had only JUST arrived at the Grubers' farm a few hours before the murders for her very FIRST day on the job. Her predecessor had suddenly quit several months earlier, and reportedly complained to others that she believed the house to be haunted.
Police initially believed that robbery was the likely motive for the crime, but that notion was quickly dispelled once large sums of money were found inside the house that would have been easily accessible to the killer(s). However, other, sordid details about the Grubers' lives led to a number of alternate theories and suspects.
Andreas and his daughter had previously engaged in an incestuous relationship, for which they had both received prison sentences (a year for Andreas and a month for his daughter). Rumors swirled that Viktoria's son Josef was the fruit of their incest. Viktoria insisted that one of their neighbors, Lorenz Schlittenbauer, was the boy's father. Schlittenbauer initially corroborated the claim, but later denied it and accused Andreas of being the father. As a result, Andreas was taken into police custody, but he was released after Schlittenbauer recanted his allegation and reaffirmed his fatherhood. At the time of the murders, Viktoria was preparing to sue Schlittenbauer for alimony.
Schlittenbauer has always been one of the leading suspects in the case. It has been theorized that, in order to deflect suspicion from Andreas, he may have agreed to pose as Josef's father in exchange for money and/or Viktoria's hand in marriage. When the Grubers failed to uphold their end of the bargain and threatened to sue for alimony, this naturally led to a lot of friction and animosity between the two households. Schlittenbauer also organized and led the "search party" that discovered the Grubers' bodies, and those who were with him later complained that he had privately accessed and possibly disturbed the crime scene.
Police also questioned whether Viktoria had actually been a widow. Her husband was reported to have been killed in WW1, but his body was never recovered. His fellow soldiers were adamant that he was killed, but that didn't stop rumors from spreading that he had secretly returned from the trenches and exacted a brutal revenge on his wife's family for her unfaithfulness. "Sightings" of Viktoria's husband would be reported through at least the end of WW2.
Although the Grubers were fairly affluent by the standards of the day, they were also notoriously thrifty. As one of their cost-saving measures, they would often employ "cheap" migrant labor to carry out any work needed on the farm. Could they have, at some point, unknowingly hired their own killer(s)?
In more recent years, some have suggested that perhaps the killer(s) motive(s) actually corresponded to the maid Maria and not the Grubers, since the murders occurred only hours after her arrival at the farm. However, it appears that contemporary investigators may have largely overlooked this line of thinking.
So who was responsible for the Hinterkaifeck murders? Was it someone with a deeply personal grudge, or simply a psychotic passerby? Did the killer(s) lurk on the Gruber property (and perhaps even secretly live in their own house) for a time before committing the murders? Sadly, although more than a hundred potential suspects have been interviewed by police over the decades (some as recently as 1986), the mystery remains unsolved to this day.
For more information on Hinterkaifeck, I recommend translating (if necessary) its German wikipedia page:https://de.wikipedia.org/wiki/Hinterkaifeck