Hundreds of children's names are etched into the wall just outside St Dunstan's churchyard in the pretty village of Cheam, carved by hand into the crumbling white stone.This is however no ordinary graffiti. These inscriptions were made by youngsters who attended a youth club at the church on the outskirts of south London in the 1980s.But far from being a hall where schoolchildren downed orange squash, ate biscuits and argued over table tennis, 'The Shed', as it was known locally, was a secret hunting ground for a man so evil he was later nicknamed the 'Warlock Paedophile'.William Lambert - who was also the church's groundskeeper and gravedigger - used the club to prey on vulnerable young girls. He claimed he was a 'warlock', a male witch with mystical powers and that he could transfer those same powers by having sex with them.One schoolgirl was terrified she might be pregnant after sleeping with her boyfriend so Lambert brainwashed her into believing he could magically get rid of her pregnancy if they also slept together. Alys* visited the club as a 13-year-old schoolgirl and can still remember the grubby sofas and tired furniture inside the ramshackle, wooden building Lambert used to entice his stream of victims.Inside, Alys and her friends could drink alcohol and smoke - freedoms they were never allowed at home and something she now understands was a grooming tactic from Lambert.The thrill of downing alcopops and puffing on cigarettes supplied by the predatory youth worker meant some of the youngsters were prepared to put up with his inappropriate comments, uncomfortable stares and occasional gropes.In an exclusive interview, she tells The Crime Desk: 'That was very common for him. Everyone just took it as that's just what he did and then he'd just laugh it off.'Now I understand, but I was very, very naïve.' Hundreds of childrens names are carved into a wall outside St Dunstan's churchyard in Cheam, south London. They were members of paedophile William Lambert's unofficial youth club there in the 1980s. Some of them belong to his victims Lambert's surname is scraped into the wall at the very top in the largest lettering on the wall Long-term missing 15-year-old Lee Boxell is thought to have been murdered by Lambert at The Shed in September 1988 and buried in the graveyard. Detectives have opened a cold case review into Lee's disappearance last month which his parents see as a 'last hope' for answersTragically, not all the children were able to walk away from Lambert's lair and the Metropolitan Police now believe missing teen Lee Boxell was among his victims.Lee, a schoolboy from nearby Sutton, became one of the most prominent missing youngsters of the period when he disappeared in 1988, with BBC Crimewatch specials devoted to him, TV appeals by the then Wimbledon footballer John Fashanu and his face printed on milk cartons.Lee remains a missing person to this day, but Scotland Yard detectives now believe his body lies in the churchyard at Cheam - buried somewhere among the ivy-covered gravestones by Lambert after he murdered him - and have launched a cold case review.Some 37 years on, Alys, now 53, still weeps at the thought of Lee's disappearance, not because they were friends, but because she thinks she witnessed the gruesome aftermath of his murder in the clubhouse - namely, a blood-soaked mattress.She says: 'There was a mattress leaning up against the wall in The Shed. It wasn't light - it looked like there was a huge stain of blood.'I know I smelled a dead body,' she recalls with tears in her eyes. 'It was rotting flesh. I had to vomit. 'I was absolutely terrified and ran home. I never ever, ever, went anywhere near there again.'Detectives and Lee's traumatised parents, Peter and Christine, suspect he may have stumbled upon Lambert sexually abusing a young girl and was killed by the paedophile before he could go to the police.'Knowing our son as we do, he would have gone for help, and maybe tried to stop him,' Peter says.Lambert, Alys recalls, did not tolerate children standing up to him and would terrify the youngsters at the club with stories of witchcraft and occult supernatural powers and unleashed a 'very calculated' web of manipulation.'He'd constantly be playing kids off of one another to drive wedges between people, so there was no trust or real friendships there,' she recalls.Lambert - who had received a custodial sentence for exposing himself to girls under 14 and impersonating a police officer in 1968 - would then identify the most vulnerable.Alys says: 'He'd talk about witchcraft and about ghosts down in the graveyard - "The Black Thing" that could hurt you if you went down there. Paedophile William Lambert was jailed for 11 years when he was convicted of raping children at The Shed in 2011 by convincing them he could transfer magical powers to them through sex The Shed has burned down years ago and a new Church Hall has been built on the site, but dreadful memories remain with Lambert's victims. Alys weeps to this day thinking of them It was here in 1988 that Alys believes she smelled Lee Boxell's rotting corpse and saw a blood-soaked mattress leaning up in The Shed. She ran home horrified and never returned until many years later'It was so people wouldn't wander around there on their own at night. He would walk you out of the graveyard. He would walk you in. He wouldn't let you just wander around after dark.'He was very controlling, so he knew always who was there, who wasn't there.'It was only at his Old Bailey trial in 2011 that it was revealed this talk of the occult was also a tactic of Lambert's to manipulate young girls into having sex with him.One woman, then aged 37, told the court Lambert convinced her that having sex with him would get rid of what she believed was her then-unwanted pregnancy when she was just 14.She said a friend already trapped in his sex ring persuaded her to visit Lambert and then she 'held my hand' while he raped her.In fact, the girl, who had missed her period by a week, was not pregnant. But she was left with the mistaken belief that Lambert's 'procedure' had worked.Another victim told the court she saw her visits to The Shed as 'a way of escaping', and that Lambert was 'lovely' to them, and gripped the impressionable girls with his talk of witchcraft.'I was fascinated,' she said. 'All my friends had problems and wanted to escape those problems.' Paedophile William Lambert pictured outside Croydon Court in 2011 facing trialThe girl said Lambert raped her more than 10 times inside a private room connected to the youth club. Once inside the room, he would lock the door, make her remove the bottom half of her clothing, and lie her on a table before drawing a red velvet curtain across her body, so she could not see her lower half as he assaulted her.Girls like this were top of Lambert's target list, says Alys today. 'I wouldn't say [he went] by looks at all. He definitely preyed on the vulnerable girls.'Once, Lambert invited Alys to The Shed on her own, she believes in an attempt to rape her.'He locked the door and I said "I don't know what's going on here, but I'm going." So then he just unlocked the door and let me walk out. But he was quite angry.'She then claims Lambert's mood towards her changed and two days after Lee Boxell's disappearance he made a chilling comment about the missing teen. Alys believes it was a warning to keep her quiet.Alys recalls: 'Bill sat me down next to my friend and told us Lee was dead and that he would never be found and he was buried not far away.'It was like he was saying if I didn't do what he wanted, the same would happen to me.'Alys immediately went to the police, but claims her report was not taken seriously.On the day of his disappearance, Lee had been due to watch Charlton and Millwall play a match at nearby Selhurst Park. But he never made it - and when he did not return home that night, concern quickly turned to panic for his parents.Peter says: 'We called the police. We called hospitals, friends, anybody we could think of. Nobody knew where Lee was.' Parents of Lee, Christine, 84, and Peter Boxell, 79, (pictured) are still searching for Lee's body 37 years after he disappeared Lee was a 'kind and considerate boy' who was 'never in any trouble', who would be the first to help those who needed it and a fierce football fan, Peter said Lee's parents have kept his room exactly how it was when he vanished. 'I wanted everything to be completely normal - unchanged', Peter saidHe continues: 'That was the start of the living nightmare. We couldn't sleep at all at night.'We couldn't leave the house for weeks in case there was a knock at the door or a ring on the telephone.'That knock or call never came. All these years later, Peter and Christine, now 84, have kept Lee's room just how he left it on the day he disappeared.'If he came home, I would want Lee to find everything exactly as it was when he left,' Peter explains.'I wanted everything to be completely normal - unchanged.'Detectives will now be re-examining what Peter describes as 'mountains' of evidence scattered across several police forces down the years. He and Christine remain optimistic.While Lambert was prison in 2012, Peter said police were tipped off that he 'was boasting that he murdered our son and buried him in the graveyard'.It led to him being interviewed on suspicion of Lee's murder. Meanwhile two other men and a woman were arrested, but no one was ever charged. The arrests sparked the biggest forensic excavation in Met Police history at St Dunstan's graveyard in hopes of finding Lee's remains.But it was unsuccessful because police were allowed to dig only in between graves and could not disturb burials. The Boxell family, pictured with Lee's younger sister Lindsay who was 13 when he disappeared Peter believes the police theory that Lee stumbled upon Lambert sexually abusing a child and thath killed him for his silence. 'Knowing our son as we do, he would have gone for help, and maybe have tried to stop him,' Some of the posters have now been taken down after being torn or faded over the years but much still remains. The couple's grandchildren now use the room when they stay but it is still known as 'Lee's Room'To this day, no one has ever been charged with Lee's murder.Lambert - a father of eight children, several of whom have spoken publicly about how he was physically abusive at home - died aged 86 in 2021 of Covid.Police say that while they don't have 'conclusive evidence' Lee was killed they believe this is the case and now their priority is to find his remains.Detective chief inspector Kate Blackburn, who is investigating the case, says: 'Lee's parents deserve answers and they deserve the opportunity to bury their much-loved son.Appealing for information, she adds: 'Your information could help end the suffering for Lee's family. If you can help, anonymously or otherwise please do get in touch.'Over the years, Peter has had to find ways to cope with the unsolved mystery of his son's disappearance.During the graveyard excavation, which he said was one of the most difficult times for him, he joined a choir formed by families of missing people. Lambert was said to have been 'boasting that he murdered our son and buried him in the graveyard' while in prison in 2012. It led to his arrest in 2014, along with three others, but he was never charged for Lee's disappearance Peter said the couple cannot properly grieve their son, not knowing exactly what happened to him, but tragically admit that 'Lee probably was murdered' Peter had the shirt Lee was wearing that day recreated by a printer. It now hangs in the wardrobe in Lee's room, along with all his other clothes Lee's remains were never found in the graveyard and Peter and Christine still don't know what happened to their sonAt a charity Christmas carol concert at London's St Martin's in the Fields, Peter sang an original song about Lee, which he said had come to him in a dream. He was met with a standing ovation.A few years later, in 2017, he performed with the Missing People Choir on Britain's Got Talent. Singing, he says, is 'really cathartic'.At home, the empty bedroom with football posters adorning the walls is still known as 'Lee's Room'. Peter often practices his singing in there, and his grandchildren from his younger daughter Lindsay - Abigail, 15, and Alex, 18 - now sleep in the room when they visit.This is a sense of a family who have long been holding their breath, waiting for answers.Peter says: 'One of the good things about the cold case team is they won't be distracted. They'll look at everything from beginning to end.'Christine adds: 'We're really, really lucky they're going to look over it again. They've got fresh eyes. Hopefully they'll find something.'*Alys's name has been changed.