The parents of a schoolboy feared murdered after going missing 25 years ago have visited the graveyard where police think he is buried.

Lee Boxell went missing from Sutton High Street on September 10, 1988, and murder detectives believe he walked to Cheam and went to an unofficial youth club at St Dunstan's Church called the Shed.

Police revealed this week they believe Lee, 15 at the time, may have seen someone being sexually assaulted in the church grounds on the day he went missing - and have called for the potential victim to come forward.

They think Lee was killed and then buried in the church grounds.

Last summer, Police began the intricate operation of excavating parts of the graveyard in a search for clues as to the fifteen-year-old's whereabouts.

Officers returned in April to extended the dig to cover most of the land behind the church on the 19th century site in an operation costing hundreds of thousands of pounds.

Gravestones have been moved, checked for clues, and returned as the Met Police carries out its biggest ever excavation.

The Boxells, Peter and Christine, visited the police at the site as part of their search for answers as to what happened to their son Christine Boxell, Lee's mother, said: "I was expecting it to be a couple of policemen with a spade, not great big diggers. It was very upsetting to see them digging for the remains of my son, I don't want them to find anything, but I do want to know what happened."

Husband Peter said the police have literally left no stone unturned. He said: "It's reassuring to know the police have never given up on finding Lee. They have thrown a huge amount of resources at it, I mean there are 30 odd policemen down there everyday looking for him."

There was one element of the visit which Mr Boxell said was particularly upsetting to see. He said: "The police have shown us a wall down the alley in front of the church which has people's initials carved on them, and that was difficult to take. It's horrible to think that Lee's initial could have been on there and has been washed away over the years."

DI John McQuade, said the wall could be important in the investigation. He said: "We believe the initials on this wall were people who used to go to the shed. I believe that another person was at the shed on the day Lee went missing and has not yet come forward.

I would urge that person, who may have been the victim of a sexual assault to examine their conscious and to speak to us. That person may hold the key to Lee's disappearance".

Anyone with information on the case can call the Metropolitan Police’s homicide and serious crime command on 020 8721 4138 or 020 8721 4005.