Police said a 21-year-old man was confirmed dead at the scene in East Dulwich, while a second male was in a stable, non-life-threatening condition.
Officers were called to the junction of Forest Hill Road and Rockells Place shortly after 3pm yesterday.
Three suspects were arrested shortly after the incident with police detaining a fourth man later in the evening.
Ian Moss, the owner of The Rose pub in Forest Hill Road, heard the shots from his office.
Moss said: “I thought it was fireworks, but it turned out to be three gunshots.”
He said he went outside and saw a man lying in the street, being treated by paramedics.
Mr Moss said there were between 50-100 people in the street at the time.
The shooting happened while the funeral of 17-year-old car crash victim Joel James Lee Morgan – also known as Jozey – was taking place.
One mourner, who did not wish to be named, said he did not think the shooting was linked to the funeral.
A woman mourner said: “We were around the grave site and he was being lowered into the ground and there was a series of gunshots fired. People didn’t know whether the noise was fireworks or not. We saw people on the other side of the fence running away.”
Scotland Yard’s Trident operational command unit, which deals with crime in London’s black communities, is now leading the investigation.
Any witnesses or those with information that may assist the investigation are asked to call 020 8247 4554 or 0800 555 111.
