Forensic archaeologists begin work at Gloucester cafe in search for South Shields teenager feared killed by Fred West
Gloucestershire Police said three forensic archaeologists have attended the Clean Plate cafe in Southgate Street, in connection with the disappearance of 15-year-old Mary Bastholm.
They are using geophysical survey equipment as part of exploratory work to see whether a full excavation of the cellar is required.
The force had received possible evidence from a TV production company to suggest the body of the missing teenager could be buried there.
Mary was born in South Shields and moved with her family to Gloucester.
She went missing on her way to catch a bus to visit her boyfriend in Gloucester, in January 1968.
Serial killer West, who died in prison in 1995 aged 53, was previously suspected over Mary's disappearance.
Along with his wife Rose, West tortured, raped and murdered an unknown number of women over a 20-year period.
It is understood that a film crew working for ITV at the location contacted police and are offering police officers full co-operation.
The production team, who have been in contact with Mary's family, are looking into claims that Fred and Rose West had more victims than those they were charged and convicted over.
In a statement, police said West had been interviewed for a total of 110 hours and had denied murdering Mary.
Gloucestershire Police said forensic assessment work would continue until Monday, before a more "considered decision" was made as to the extent of excavation.
"Three forensic archaeologists have attended the Clean Plate cafe and are in the cellar in order to continue with assessments," a police spokesman said.
"They are using geophysical survey equipment and in order for this work to be done a fireplace needs to be dismantled.
"We can confirm the ongoing activity at the location on Thursday relates to ongoing assessments and not excavation work."
Police also defended the decision in 2012 not to excavate the cafe, as there was "insufficient evidence" the teenager was buried there.
Family liaison officers are now providing support and updates for Mary's family.
In a statement, her family said: "We are aware of the ongoing developments around Mary's disappearance and are being kept up to date and supported by Gloucestershire Police family liaison officers."
It is understood that Mary's brother, Peter Bastholm, died last year.
Speaking in 2014, he had called on Rose West to say what happened to his sister.
He told Sky News at the time: "I think Rose knows exactly what happened to Mary because I assume she and Fred discussed it between themselves. Whether she will ever disclose it, I really don't know."
Mary's disappearance in 1968 was at a time when Fred West, who often did jobs in the street where she worked as a waitress in a cafe, was abducting girls in Gloucester.
West is said to have confessed, in conversation with his son Stephen, to killing Mary, but never admitted it to police.
Mary's body was not found during the 1994 excavation of the Wests' home, now known as the "House of Horrors", on Cromwell Street in Gloucester.
West was charged with 12 murders, but took his own life in a Birmingham prison before his trial.
Rose West was convicted of 10 murders in November 1995 and is serving life.