A mother arrested on suspicion of murdering her three-year-old daughter in Birmingham remains in custody, being quizzed by detectives.
Officers arrested the woman, in her 20s, after the youngster's body was discovered at a house in Milverton Road in the Erdington area of the city at 5.30pm on Saturday.
A cause of death has not yet been established but a West Midlands Police spokeswoman said a "hazardous substance" was recovered from the address, adding: "Further toxicology and forensic tests are being carried out to see if the hazardous substance caused or contributed to the child's death."
Neighbours in the tree-lined street, which backs on to a reservoir, said detectives had been making door to door inquiries asking residents of they kept corrosive substances at their properties.
Adam Cotterill, 18, who lives opposite the terraced home where the girl's body was discovered, said: "Two detectives came round and asked my dad if we had any corrosive substances in the house, like acid. If that's what they think killed her, it doesn't bear thinking about."
Another neighbour said: "They (police) asked if I had anything hazardous and I said bleach but they said they were talking about much stronger chemicals than that."
Police have not yet named the girl and said they would only identify the woman in custody if she was charged, but sources confirmed that the pair were mother and daughter. A police spokeswoman said family liaison officers were supporting their relatives.
Chief Inspector Mark Payne said: "The death of this little girl in suspicious circumstances has led to an immediate and comprehensive investigation. Detectives, forensic experts and local officers are working together to establish how the girl died and who is responsible. We are working together with the local community, who have been shocked and distressed by this death."
Neighbours described the child as a "pretty, playful little girl", who had lived at the rented property with her mother for around a year. It is believed the woman was a single mother, though neighbours said a man in a black Audi sports car visited frequently.
Helen Gilfoyle, a 42-year-old teacher who lives a few doors away, said: "Nobody really knew them, they kept themselves to themselves. I don't know whether that was just the woman's nature or if down to the language barrier because I think she only spoke broken English. She was lively, like any other three-year-old. She was such a pretty little thing too, beautiful.
"She was a pretty, playful little girl and whatever has happened, whatever the circumstances it is desperately sad because she was just three years old."
The house remained cordoned off and a lone police officer stood alongside a blue forensic tent on the front lawn. Three bunches of flowers had been placed at the base of a tree in front of the house, along with the message: "Rest in peace, little angel."