Fred West told police he was involved in Mary Bastholm's abrupt disappearance, but he reportedly told others a completely different story.
The 15-year-old was working as a waitress in the the Pop-In cafe in Gloucester, now called the Clean Plate cafe, which was just half a mile from the West's house of horrors at 25 Cromwell Street.
Fred was known to be a customer at the cafe around the time Mary vanished in January 1968 and there is also speculation he may have done renovations to the building.
After having tea with her parents, Mary went out with a carrier bag containing a Monopoly set at 7.15pm and was set to catch the 7.25pm bus.
She had arranged to meet her boyfriend five minutes later but she was not on the bus, then he suspected something was wrong when she wasn't on the following one either.
Sadly, neither Mary's parents or her boyfriend ever saw her again - and the teenager's body has never been found.
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West was known for picking up victims at bus stops, so the theory emerged that he had offered Mary a lift before murdering her.
A team of private investigators working as part of ITV documentary Fred And Rose West: Reopened uncovers a previously unseen documents including a witness statement from Fred West's 'appropriate adult' - Janet Leach.
Fred told police he was not involved in Mary's disappearance at all, but Leach claimed he confessed to knowing she was killed and who was responsible.
Her statement reads: "He told me many things which he would not tell the police. Fred spoke about Mary Bastholm. He said he picked her up but did not kill her. John and Rose killer her."
Leach's full statement was never read out during the trial or made public until now. She did not wish to speak to the programme.
The investigating team also spoke to Chris Roberts, who remembers Mary and believes West did some work in the basement.
He says: "Mary went missing in January 1968. In the week following that, on two occasions I walked down the road, 50 yards from where I worked and saw Fred removing what I would say, looked like concrete bags or sand bags from his van, putting them over his shoulder and carrying them into the cafe.
"It wasn’t until latterly that I realised what could have happened."
DCI John Turner, who is the senior investigating officer on the case, says they do not know for certain whether West did basement renovations or not.
Led by Former Detective Chief Inspector Colin Sutton, the team conducted their own search in the basement of the cafe in May this year.
Using an endoscopic camera to look under the concrete floor, they discovered evidence of some buried blue material, which was alarming as Mary was wearing a blue coat and cardigan when she went missing.
They immediately alerted Gloucestershire police, who then launched a major investigation to excavate the footings using ground-penetrating radar and sniffer dogs to look for human remains.
It was a tough time for Mary's family, with her niece Helen Davies revealing her father carried a picture of her everywhere in his wallet until the day he died.
Helen says: "It’s just so sad. Really sad. I’m just amazed, I can’t believe it after so many years. And hoping that we’ll finally get some sort of closure."
During day seven of the search, the police find the source of the blue material from a smashed pipe, which has given the appearance of blue material.
They continue searching around the anomalies in the basement but conclude Mary's remains are not present underneath the floor.
DCI John Turner, senior investigating officer of Operation Tryfan, says: "I'm disappointed, with the family, that I couldn't find her. I don't know where Mary is."
After three months of investigation, the documentary team handed their findings to Gloucestershire police who initiated a new operation into their findings. The investigation is ongoing.
Sadly, Mary's parents both died before they were able to get closure and discover what happened to their daughter.
Her dad Christian eerily predicted that she was taken by "someone she knew" at the cafe.
Asked about her disappearance two years after she vanished in 1970, Christian said firmly: "It is rather difficult to say, but one thing I will always say is this – she did not go away on her own.
"For a young girl like that to evade the police for so long well she’d have to be a master of the game wouldn’t she?
"Personally I think she took a lift from someone she knew, this could have been someone perhaps who came into the cafe."
In May this year, Mary's boyfriend at the time of her disappearance, Tim Merret, told the Mirror he has no doubt Fred killer Mary but doubted she was buried under the cafe.
"To me it doesn’t make sense that she is there but I would urge the police to keep looking for her," explained Tim.
"I’ve never forgotten Mary, she was my girlfriend for about six months when she just disappeared.
"She was coming up to her 16th birthday When Fred West was caught it was obvious to me that Mary was one of his victims.
"He didn’t give up the names of everyone he killed and I believe Mary was one of those."
*Fred and Rose West: Reopened is on ITV at 9pm on Wednesday and Thursday
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