Carlotta Brett-Pierce (inset) was arrested in connection with the death of her 4-year-old daughter.
Brooklyn prosecutors have launched a criminal investigation of the city's child welfare agency and its outside health and social service providers responsible for monitoring the 4-year-old girl who died in September.
District Attorney spokesman Jerry Schmetterer said Friday the office had begun investigating the Administration for Children's Services.
Marchella Pierce's 18-pound body was found Sept. 2. Marks on her ankles and rope discovered on a bed led investigators to believe she had been bound.
The girl's mother faces charges of assault and endangering the welfare of a child. Her attorney didn't immediately return a message.
ACS spokesman Michael Gagan says the agency will cooperate with the investigation.
District Attorney Charles J. Hynes said the 2006 beating death of 7-year-old Nixzmary Brown was a factor in his decision to investigate.