After finding a dead and a living baby in Halle an der Saale within a week, the investigators ruled out a relationship between the two girls.
Forensic medical examinations had shown that they could not be siblings, the police said on Wednesday.
The second baby, discovered last week, is healthy and is being adequately cared for.
The surviving girl was found last Wednesday on the stairwell of an apartment building in a blue-gray baby footmuff.
At the time of the discovery, the infant was only a few hours old, according to the police report.
The girl's parents are being searched intensively.
Two days earlier, a dead baby was discovered on the premises of a waste disposal company in Halle.
An autopsy showed that the child had lived after birth.
The public prosecutor's office started an investigation.
In both cases, the police asked the population for help and launched an appeal for witnesses.