Flowers have been left outside the building a baby fell from in central London.
Officers were called to the Peabody Estate on Horseferry Road, Westminster, at roughly 7.30am on Saturday.
The baby girl, 18 days old, was taken to hospital where she was pronounced dead, the Metropolitan Police said in a statement.
Later on Saturday, forensic officers were seen working at a window in a flat on the building's third floor.
And by Sunday flowers and a toy animal have been propped up against the building in tribute.
A 43-year-old woman was arrested on suspicion of murder at the scene and taken into police custody, where she remains.
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Detective Chief Inspector Alison Foxwell, who is leading the Met's investigation, said: "The death of an infant is always an extremely tragic occurrence, and officers are making urgent inquiries around the circumstances.
"At this stage, we believe the incident occurred within a domestic context, but we are appealing for anybody with information to come forward."
A spokesperson for the London Ambulance Service said the baby was treated at the scene before being taken to a major trauma centre.
The street is home to government buildings, including the Department for Transport's offices, as well as Channel 4's headquarters and multiple residential addresses.
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