In the case of the six-year-old rescued from a river from Halle in Saxony-Anhalt, investigators found a 24-year-old suspect.
He was provisionally arrested at noon at his workplace, the police said.
There was "urgent suspicion" of the man, it said.
There were several indications from the population, a spokesman for the Halle public prosecutor had previously said.
A nine-member investigation team called "Elsa" has been dealing with the case for days.
Two published phantom images should also lead to the suspect.
Calls for help from the icy hall
The suspect is said to have carried the six-year-old mostly in his arms through the city center early on Sunday morning.
Later the girl was saved from drowning by two joggers from the hall.
What exactly happened that morning is still unclear.
For tactical reasons, the investigators did not want to comment on whether it was a kidnapping or another criminal act.
The girl lives with her parents in downtown Halle.
On Sunday, the child was last seen in the family apartment at around 7:30 a.m. and then reported missing.
At around 8.30 a.m., the two joggers found the girl in the icy hall after they heard cries for help.
Icon: The mirror
wit / dpa