The Alexander Family.
Harald and Dagmar Alexander were a married couple living in Dresden, Germany, and part of the 'lower birth society', which was a tiny religious cult. The leader of the group contended to be a prophet and the voice of God on earth, and after the leader's demise, Harald contended he inherited the prophet-hood.
In 1954, the couple had their 2nd child, Frank. Harald then asserted that Frank was the prophet, and everything Frank said was to be accepted as the word of God and law, and must be fulfilled by all within the devotees and family. This comprised his older sister, Marina, and his younger sisters, Sabine and Petra, who were twins.
When Frank became a teenager is when things took a twist towards the disturbed. He ruled that having sex with someone outside of the family was impure and sinful, and decreed that his family only have intercourse with each other, this comprised his mother and sisters. Amazingly, they all agreed because they believed it was their way of serving God.
Rumours about the family started to circulate locally, and when police started to investigate them, the Alexanders packed up and strode to the Canary Islands. There they lived a private life and the neighbours didn't know much about them, but for the fact that they fiddled organ music during the day and night.
By December of 1970, the family had been in the Canary Islands for 10 months, and on the 22nd of December, Sabine was working as a cook at the palace of a Doctor. The Doctor was amazed when Harald and Frank entered the villa caked in what seemed to be mud. They asked for Sabine to come out so they could talk to her, and when she did, that's when the Doctor overheard them saying:
"Sabine dear, we wanted you to know at once that Frank and I have just completed killing your mother and your sisters"
One would think that upon hearing such morbid news, she would have screamed or run away, but rather, she grasped her father's blood-stained hands and said:
"I'm sure you've done what was necessary."
Harald then noticed the doctor was there and turned to him and admitted:
"Ah, you've overheard. We've murdered my wife and other daughters. It was the hour of killing."
The doctor said the lasting members of the Alexander family to wait on his front patio, he ran inward and called police. The police took Harald and Frank into custody and investigators reached their apartment, to which they "found out the most gruesome spectacle we had ever seen". Blood was dabbled everywhere, and in the living room were the bodies of Marina and Petra, their breasts and genitals were cut-out and nailed to the wall. Dagmar had been discovered in the bedroom and underwent the same grizzly fate as her daughters.
Upon querying, Frank contended he killed his mother with a clothe-hanger first because she "looked at me wrong", and upon seeing the bloodshed, Harald contended it "was the hour of killing" so he played organ music while his son was massacring and destroying his family.
Both father and son contended that the women of the family knew and adopted their roles in the foretold "hour of killing" which Frank had asserted over the years could come at any moment, and stayed remorseless because they claimed they sent the women to paradise. Both were considered unfit to stand trial due to mental health issues and were sent to a psychiatric hospital to stay there until death takes them. Sabine altered her name and ended up living with a coven, and her whereabouts are unknown.