A 14-year-old teenager was killed in a violent act in Middle Franconia on Friday.
Her 41-year-old mother suffered serious injuries.
The girl's brother is suspected of murder.
The 17-year-old was temporarily arrested on Friday shortly after the crime "near the scene of the crime", as a police spokesman said.
On the morning of Epiphany, a public holiday in Bavaria, the police rushed to the well-kept residential area in Weisendorf near Erlangen.
An emergency call was received - "from the environment" of the family, as the spokesman said.
The police found the girl in the house.
According to the first impression, the 14-year-old died from a pointed, sharp object, probably a knife, as the spokesman said.
The mother was taken to the hospital with serious injuries, but her life was not in danger.
According to initial findings by the police, the woman and the two young people were alone in the house at the time of the crime.
The police did not provide any information about the father of the children.
Exactly what happened in the house, whether there was a loud argument, whether the mother or daughter was attacked first, whether the son wanted to flee or was willing to be arrested - all of that initially remained in the dark, as did a possible motive.
The investigation is still in the early stages, the spokesman said.
In the afternoon, forensics experts were still working in their white uniforms in the semi-detached house, and numerous police forces were on site.
They also saw possible traces of blood outside the house and also in the area of the neighboring house.
It was initially unclear what it could be about.
The crime scene and the street in front of it were cordoned off.
There were no neighbors from the neighboring houses to be seen.
Only a few people walked by.
Weisendorf has 6800 inhabitants.
In the afternoon, a candle stood near the crime scene.
A black bow was tied around it and a red rose attached to it.