The man seen on CCTV is described as dark skinned, with a full beard, wearing a light baggy top with a satchel across his chest.
Detective Chief Inspector Sheila Stewart said: "It is vital we track down this man who was in the precise area at the time Mariana was attacked and killed."
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A bright and sunny day tomorrow, but feeling distinctly cool and chilly tonight.
An ITV News London investigation has discovered the inquest will now be held at Westminster Coroner's Court.
The family court finalised the adoption as the criminal proceedings were still under way. The couple have vowed to fight for their child.