Police investigating the murder of Ryan Musgrove on 16 July 2009 have offered a £20,000 reward on the third anniversary of his death.
Officers want information relating to a gunman who was seen riding a bike around the murder scene in the days leading up to Mr Musgrove's death.
Police describe the man as a white, with a slim build, wearing dark clothing, possibly a balaclava, a cycling helmet, goggles or sunglasses and a face mask.
He left the scene on a black mountain bike in the direction of New Addington, Croydon.
In the days leading up to the murder detectives know that the suspect was seen on 9th July at 6pm at Coney Hall Recreation Ground. He was seen again on 13th July between 4.30pm and 5pm
On 14th July, the suspect was seen at 6.30pm at Sparrow Den playing fields. Two days later on 16th July he was seen again between 6pm and 6.30pm when Ryan was shot.
The gun used in the murder was a Luger P8, a World War Two German issue firearm. Detectives say it is an unusual weapon and very distinctive.
Police are urging anyone with information to get in touch.