David, 57, was jailed for life last year while his 52-year-old wife was sentenced to 12 years in prison after they subjected 10 girls and boys to a string of horrific rapes, sexual assaults and beatings.
The prolific abusers became friends of the Wests when they lived close to their notorious home in Cromwell Street, Gloucester, in the 1980s and 90s.
David terrified some of his victims by boasting of his connections to the serial killers, who used to drink at the Prince Albert pub which he ran in Gloucester.
Scaffolding was erected in the garden at the council bungalow where the Williams last lived before they were jailed, and a make-shift roof put up, apparently to stop people seeing the scene.
The source said: "A person close to the abuse came forward to make allegations to the police that some years ago a baby was murdered."
"The police are now digging up the garden at the bungalow over the next few days to see if there are any remains and to see if this allegation has any truth in it."
Police confirmed the operation related to 'historic information' relating to the former occupants.
Neighbours said they had heard noises coming from the garden which sounded like digging, while some officers have been seen with pickaxes.
One onlooker said: "The garden is not visible from the road but you can clearly hear what is going on. The whole village seems to be in shock."
A next door neighbour said: "We just thought they were normal people.
"We did not know anything about it. The first we heard was when someone told us they had seen it in the news online and we looked for ourselves."
An unnamed neighbour added: "I saw them from time to time. They looked a bit odd.
'When it all came out everyone was really shocked. There was a lovely couple living there before."
Suzanne Cox, 47, self employed mother-of-five, said: 'They were an odd couple. I made an effort to say hello but I wish I hadn't. She was very solemn. You could tell she didn't want to get involved with other people."
The historic offences by the Williams were committed between 1991 and 2004 while the couple lived in both Gloucester and in Exeter, Devon.
For part of the time, the pair lived in Cromwell Road and David had previously boasted of a friendship and connection to the Wests, who were locals at his Prince Albert pub in the 1980s and 90s.
But what was described in court last year as the couple's 'façade of innocence' was blown open in July 2013 when a woman disclosed to a mental health professional that she had been raped and sexually abused by David Williams when she was 15.
She then spoke to Detective Constable Debbie Dow, from the force's child abuse investigation unit, and made a complaint against David Williams.
A number of other victims then came forward to uncover the abuse they had been subjected to at the hands of Williams and his wife.
The couple denied all allegations against them throughout the investigation and the trial, despite overwhelming evidence against them.
But after a jury heard harrowing evidence of rape, sexual assault and violence, the pair were found guilty of a string of charges after a six-week trial at Exeter Crown Court.
