Police are appealing for a witness to contact them as they believe he may be able to assist enquiries into how a man was seriously injured in a fall from a window in Brixton Water Lane yesterday (6 April) afternoon.
The witness was seen to tend to the injured man immediately after he had fallen and was heard comforting him.
But he left before an ambulance and police officers arrived.
He is described as a black man, aged between 30 and 40, of slim build and was wearing a dark hooded coat or jacket.
Investigating officers are keen to speak with to him as he may have valuable information.
A 28-year-old man was taken to a south London hospital with head injuries; he remains in a serious but stable condition. Next of kin have been informed.