Hinterkaifeck was a small farmstead situated between the Bavarian towns of Ingolstadt and Schrobenhausen, approximately 70 kilometres (43 mi) north of Munich. On the evening of 31 March 1922, the six inhabitants of the farm were killed with a mattock. The murders remain unsolved.

The six victims were parents Andreas Gruber (63) and Cäzilia (72); their widowed daughter Viktoria Gabriel (35); Viktoria’s children, Cäzilia (7) and Josef (2); and the maid, Maria Baumgartner (44).

Hinterkaifeck was never an official place name. The name was used for the remote farmstead of the hamlet of Kaifeck, located nearly 1 kilometre (0.62 mi) north of the main part of Kaifeck and hidden in the woods (the prefix Hinter, part of many German place names, means behind), part of the town of Wangen, which was incorporated into Waidhofen in 1971.

Strange things began to occur in and around Hinterkaifeck sometime before the attack. Six months before the attack, the family maid quit, claiming she heard strange sounds and that she believed the house to be haunted. Andreas Gruber found a strange newspaper from Munich on the property in March 1922. He could not remember buying it and thus Gruber initially believed that the postman had lost the newspaper. This was not the case, however, as no one in the vicinity subscribed to the paper. Just days before the murders, Gruber told neighbors he discovered tracks in the fresh snow that led from the forest to Hinterkaifeck. While this alone was not unsettling, it was the fact that the tracks did not lead away from the house again that unnerved him. Around the same time, one of the family’s house keys went missing. The family also repeatedly observed a man with a mustache. During the night they heard footsteps in the attic, but Andreas Gruber found no one when he searched the building. Although he told several people about these alleged observations, he refused to accept help and the details went unreported to the police. According to a school friend of the seven-year Cäzilia Gabriel, the young girl reported that her mother Viktoria had fled the farm the night before the act after a violent quarrel and only hours later had been found in the forest. 33 years later, the school friend’s story had changed and she claimed that not Viktoria Gabriel, but her mother, Cäzilia Gruber, had fled.

On the afternoon of March 31, 1922, a Friday, the new maid, Maria Baumgartner, arrived at the farm. Her sister had escorted her there and left the farm after a short stay and she was most likely the last person to see the inhabitants alive. A few hours later, the six inhabitants of Hinterkaifeck would be dead. It is impossible to reconstruct the exact events of the evening without some speculation, but some details are clear after investigation. It appears that in the late evening, Viktoria Gabriel, her seven-year-old daughter Cäzilia, and her parents Andreas and Cäzilia Gruber, were lured to the family barn through the stable, where they were murdered, one at a time. The perpetrator (or perpetrators) used a mattock belonging to the family farm and killed the family with blows to the head. It is unclear if the family went to the barn as part of a regular routine, or if something out of the ordinary caused them to visit this part of the estate. Later experiments proved, however, that screams from the barn could not be heard in most of the rest of the estate. The perpetrator moved from the barn through the stable into the living quarters, where – with the same murder weapon – he killed the young maid Maria Baumgartner in her bedchamber. Presumably, he killed young Josef last, as the two-year-old boy slept in his bassinet in his mother’s bedroom.

Four days passed between the murders and the discovery of the bodies.

On April 1, coffee sellers Hans and Eduard Schirovsky arrived in Hinterkaifeck to place an order. When no one responded to the knocks on the door and the window, they walked around the yard but found no one. They only noticed that the gate to the machine house was open before they decided to leave. Cäzilia Gabriel was absent without excuse for the next few days of school and the family failed to show up for Sunday worship. On Monday, April 3, the postman, Josef Mayer, was delivering the mail at Hinterkaifeck when he noticed that Saturday’s mail was still where he had left it, and that no one had been in the yard. Assembler Albert Hofner went to Hinterkaifeck on 4 April to repair the engine of the food chopper. He stated that he had not seen any of the family and had heard nothing but the sounds of the animals, noting the barking dog. After waiting for an hour, he decided to start his repair, which he completed in roughly 4.5 hours. After the repair, he noticed that the barn door was open, but could not say for certain whether it had been open when he got there. He peeked into the barn but did not go inside. In Gröbern, he met the daughters of the village guide, Lorenz Schlittenbauer, and told them that the repairs in Hinterkaifeck were done. Hofner also told Georg Greger, the mayor of Wangen, about the ghostly emptiness of Hinterkaifeck. Schlittenbauer then sent his two sons Johann and Josef to Hinterkaifeck to see if they could make contact with the family. When they reported that they did not see anyone, Schlittenbauer headed to the farm the same day with Michael Pöll and Jakob Sigl, at which time they discovered the mostly concealed bodies in the barn and home.