Officers are searching a cafe following reports a body could be buried in the building.
Police say the search at the The Clean Plate cafe in Southgate Street, Gloucester, is linked to the disappearance of Mary Bastholm, who was feared a victim of serial killer Fred West.
Mary was 15 when she was reported missing on January 6, 1968, but her body was never found.
It comes after a production company was filming a documentary and found possible evidence to suggest a body could be buried in the building.
Assistant chief constable for Gloucestershire Constabulary, Craig Holden, said: ‘This could be a significant development on a case which has gained a lot of public interest over the years.
‘On the basis of the information provided to us, we consider this to be new and potentially important evidence in the case of Mary Bastholm, however further detailed assessments will take place over the following few days to determine the extent of excavation needed.
‘First and foremost our thoughts are with Mary’s family and we would ask that their privacy is respected at this difficult time.
‘This news may understandably alarm those who work near to the premises, as well as those in the wider Gloucester community and beyond.
‘The Constabulary has always said any fresh evidence would be reviewed. This has happened and a focused and proportionate investigation will now take place.
‘Due to the potential scale of this there will likely be some disruption to those who work nearby, and I ask for their patience and co-operation during this time.
‘We will have local officers in the area and a visible police presence at the location possibly for a number of weeks.
‘We would also encourage anyone who is affected by this news to please seek support.’
She has previously been linked to the property, and her disappearance was also previously linked to serial killer Fred West.
There was suspicion he was involved in her death.
Officers are expected to remain at the property for several weeks.
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