system
A chat on 4chan
human
Its been solved. There was a German documentary where they proved it was some old fuck that was screwing the daughter. They never busted him even though they suspected him because he was already so old and sick.
gpt
>some old fuck that was screwing the daughter
kind of, but the real story behind gets a little deeper.
So the daughter was about 34 years at the time of the murder, mother of two. The youngest son was probably due to the incestious relationship with her father - the other guy wanted to marry the daughter (widdowed due to WW I) until he found out. The father was sentenced for blutschande (= incest) before and they agreed that he would legally accept the kid as his, so the father wouldn't go to prison again and he was promised that the would be allowed to marry the daughter (wich the father declined before and was legally needed in that time to marry).

So then the father declined again because he was over posessive of his daughter - the murderer dude first wanted to claim about the incestious child again and go to the local police, to wich he received a lot of money not to do so by the daughter. It's not really clear why he still murdered all those people but the person could never be legally charged because of lack of foundation and evidence.