The garden of a property where double-killer Christopher Halliwell once lived is being searched by police.
Officers are digging at two addresses in Broad Street, Swindon. The work is expected to take five days.
Taxi driver Halliwell was jailed for life last year for the 2003 murder of Becky Godden, having already admitted killing Sian O'Callaghan in 2011.
Wiltshire Police said the excavation was related to new intelligence the force had received.
Det Ch Insp Jeremy Carter said: "Searches are being conducted in the gardens and garages of two properties in Broad Street over this coming week.
"Whilst we do not have plans, at this stage, to search inside the properties, there will be some disruption to the occupants.
"I would like to make it clear that those living at the addresses have no involvement in the investigation and we thank them for their understanding and patience."
Several security staff are guarding the scene of the search and a black tarpaulin has been erected across an alleyway by the house along with white tents.
One resident, who did not wish to be named, described the street as "quiet".
He said the occupants of one of the houses - where Halliwell lived with ex-wife Lisa between 1997 and 2001 - changed frequently.
A local shopkeeper added: "I used to work in a petrol station and [Halliwell] would come in to buy his petrol and diesel. He was quiet, normal."
BBC West's home affairs correspondent Charlotte Callen said one potential line of police inquiry is the disappearance of Sally Ann John, who was working as a prostitute when she went missing from Swindon, aged 23, in 1995.
She lived close to the killer at the time.
Halliwell was jailed for life in 2012 for the murder of Miss O'Callaghan, 22, and was told he must serve at least 25 years in prison.
He was convicted of murdering Miss Godden, 20, last September and given a whole-life sentence.
Halliwell evaded justice for five years in relation to Ms Godden's death due to police breaching arrest guidelines.
While offers were investigating the disappearance of Ms O'Callaghan, Halliwell offered to take police to "another one" and led officers to a field in Gloucestershire, where Ms Godden's remains were found.
However, arrest guidelines were not met so his confession was inadmissible when the case first went to court.