A £20,000 reward is being offered to anyone who can help find a 15-year-old boy who went missing 26 years ago.
North Cheam boy Lee Boxell has not been seen since he went missing in 1988.
Now police are offering the reward in exchange for any information that leads to the recovery of Lee's body and prosecution of those involved in his disappearance.
Police have announced the reward days ahead of what would have been Lee's 41st birthday on Sunday, February 16.
Detective Inspector John McQuade, leading the investigation, said: "We have been trying to solve the mystery of Lee's disappearance for 26 years now and have carried out extensive enquiries and appeals over the years.
"There are two working theories - that Lee was the victim of a sexual assault that resulted in his death or that he intervened to try to help someone else and was then assaulted.
"We hope the offer of this reward may encourage people who have not previously felt able to come forward to now do so. Someone knows what happened to Lee and where his body is buried.
"We are still appealing for any victim of sexual assault around that time, linked to the area or the shed, to please contact us in confidence.
"They could hold information vital to our investigation that would help us piece together Lee's last movements."
Lee's dad Peter Boxell, who performed a moving song entitled Where is Lee at the charity Missing People's carol service in December, added: "I am pleased the police are funding this reward and would appeal to anyone with information to come forward.
"We, Lee's family, need answers to what happened to Lee. Someone in this community can give us those answers. Please help us bring Lee home."
LISTEN TO 'WHERE IS LEE?' BY PETER BOXELL
The last known sighting of Lee was in Sutton High Street at 2.20pm on Saturday, September 10, 1988.
Lee was thought to be on his way to a football match at Selhurst Park but never attended the game.
Police investigations have led them to believe Lee may have attended an unofficial youth club in an out building at St Dunstan's Church in Cheam known as the Shed where young people could get together to drink and smoke.
Police have excavated St Dunstan's Church yard as they search for clues
Detectives believe it is possible he could have gone there on the afternoon he went missing and come to some harm.
Officers also know of a paedophile ring that operated in the Cheam area at the time.
Det Insp McQuade added: "We are particularly keen to speak to anyone who knew Lee or can place him at the 'shed' at the time he disappeared. We do believe someone else was there that day.
"If you can help please come forward."
Anyone with information can call the incident room at Sutton police station on 0208 721 4005 or the charity Crimestoppers on 0800 555 111.
- Ben Butler trial: Ellie Butler's mother admits lying about her death 'to protect an innocent man'
- Firefighters hand out sandbags to homes at risk of flooding after heavy rainfall
- 'Grave concerns' for boy missing with mother for a year as High Court judge issues appeal
- Britain's Got Talent: Wayne Woodward makes it through to Saturday's final
- Truly stunning - 24 of Tim Peake's most amazing photos from space