SPECIALIST resources have been drafted in to support the major forensic investigation underway at the former home of double murderer Christopher Halliwell.

Wiltshire Police have confirmed that experts from outside the force are working alongside their officers as the complex exploration of yards and garages behind two Broad Street properties continues.

The operation was launched on Monday after detectives received information they felt warranted a significant deployment of resources for a week-long excavation in search of evidence.

A spokesman for Wiltshire Police said: “We currently have a number of crime scene investigation specialists, detectives and other officers involved.

“This equates to a maximum of 10 staff involved at this time, which also includes a number of external forensic experts.

“The searches are being carried out to allow us to look for items of interest in relation to an ongoing investigation by the Brunel Major Crime Investigation Team.

“Searches of this nature are not carried out routinely, however they are appropriate given the information that we are responding to.”

The major crime team is a tri-force initiative made up of officers and staff from Wiltshire, Avon and Somerset and Gloucestershire.

The unit specialises in the investigation of cases involving murder and manslaughter as well as other serious and complex crime where appropriate.

Wiltshire Police are refusing to comment on which of those areas of expertise this ongoing investigation comes under.

Leading forensic expert Kimberlee Moran, who launched the Centre for Forensic Science at University College London, has written extensively about the complexities involved in excavations such as that being undertaken by police in Swindon.

Outlining why the police place great value on the involvement of outside experts, she said: “Excavation without the proper training can often lead to horrific results such as the loss or destruction of evidence.”

In cases where the investigation involves a search for human remains, she said: “Usually by the time a forensic archaeologist gets involved, a grave has already been found.

“However in some cases, the police know a grave is in the immediate area, i.e. a small field or back yard, but do not know the exact spot.”

She outlines how officers may go about examining an area of interest, including looking for obvious signs such as disturbed earth or dying vegetation and more subtle indications such as indentations in the ground caused by the slumping of soil during body decomposition.

The removal of wheelie bins marked with concrete and soil labels indicates that much of what is being excavated from the Broad Street site is being taken away from the area for further analysis.

But Ms Moran suggests the process if far more complex than simply removing soil from the ground to be transported elsewhere.

She said that forensics teams must “be on the lookout for changes in soil colour, consistency, other cuts, anything that might signify a new context”.

Describing the whole process as “methodical and detailed”, she outlined the need to sift through the soil, to measure and mark the location of any items discovered, to photograph the site, and to log every step taken.

She added: “Often it is the tiny bits of evidence that end up being the most important. Things like cigarette butts, coins, scraps of paper, teeth, rings, fibres and glass can be hard to find but contain a wealth of information.”

While Wiltshire Police has said their investigation is likely to last until the end of the week, it could well take more time than expected.

A spokesman said they hope to be in a position to release more information around timescales on Thursday.

The force has been keen to emphasise that the ongoing operation is not related to the current occupants of the two Broad Street homes.

They have also refused to be drawn on whether it is linked to the convicted double murderer, Christopher Halliwell, who lived in one of the houses at the centre of the search, 96 Broad Street, between 1997 and 2001.

The 53-year-old former taxi driver is currently serving a whole life sentence for the murder of two young women from Swindon.

He killed 20-year-old Becky Godden in January 2003 and 22-year-old Sian O’Callaghan in March 2011.

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."