Police search for more bodies in garden of double killer
Halliwell, 53, of Swindon, Wiltshire, murdered Becky Godden, 20, in January 2003 and Sian O'Callaghan, 22, in March 2011.
He was handed a rare whole-life order - meaning he will never be released - at Bristol Crown Court in 2016 after being convicted of Miss Godden's murder.
Following his sentence, police said there was a "distinct possibility" that Halliwell was a serial killer, highlighting the eight-year gap between the murders.
Wiltshire Police began searching the gardens and garages of two properties on Broad Street - where Halliwell lived - in Swindon on Monday.
A force spokeswoman said: "Work at the addresses in Broad Street is expected to last five days. This intelligence-led activity is part of an ongoing investigation."
Detective Chief Inspector Jeremy Carter, who is leading the investigation, said: "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."
Halliwell abducted office administrator Miss O'Callaghan as she walked home following a night-out in Swindon and dumped her body in Uffington, Oxfordshire.
He then confessed to killing another woman, a prostitute he had picked up from Swindon, had sex with and strangled in January 2003.
The father-of-three led police to a field in Eastleach, Gloucestershire, where Miss Godden's remains were discovered.
Last year, it emerged that Halliwell had spoken of his desire to become a serial killer in 1985.
In a phone call from prison, he allegedly claimed that officers wished to interview him about eight murders.
Speaking outside Bristol Crown Court last year, Detective Superintendent Sean Memory said: "He talked candidly in 1985 about wanting to be a serial killer and I genuinely believe that's a distinct possibility."