The incident happened around 7 p.m. in the Bedford-Stuyvesant section.
The 5-year-old girl was being watched by a 25-year-old man that neighbors say is the girl's stepfather, who left the bathroom for a few minutes and returned to find the girl unconscious.
She was rushed to Brookdale Hospital, where she was pronounced dead.
The medical examiner has yet to determine the cause of death.
The man was being interviewed by police, but no charges have been filed. The man said that moments before the incident, the child was talking and that nothing seemed out of the ordinary.
Sources say officers have had contact with the family in the past, and that the girl had some kind of medical condition that may have impacted her equilibrium.
That is now a part of the investigation.
Authorities are trying to determine if any sort of crime was committed or if this was just a tragic accident.
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