Police investigating the murder of office worker Sian O'Callaghan are probing links to a 1996 murder and a Wiltshire missing woman case - as the hunt for a second body continues.
Officers revealed the second body could relate to an incident several years ago, and could be an adult.
Chief Superintendent Steve Fulcher, leading the inquiry, said: "If there is a second body, we believe it relates to an incident some years ago and it is an adult.
"Wiltshire only has one outstanding missing adult case and that is from several years ago."
It is understood teams investigating the murder of Melanie Hall, 25, in 1996, are to liaise with officers in Wiltshire, while the 2001 disappearance of another woman in the county is also being looked into again.
Hospital clerical worker Melanie Hall disappeared after leaving a nightclub in Bath, and her remains were found in a bin liner beside the M5 in Gloucestershire in 2009. Nobody has ever been charged with her murder.
Miss O'Callaghan's body was discovered on Thursday near the famous "White Horse" landmark in rural Oxfordshire.
Police have not yet revealed the cause of her death, but a post-mortem is being carried out.
A 47-year-old man - named locally as minicab driver Christopher Halliwell - is also being held in custody on suspicion of two counts of murder and a kidnap, after being arrested at a Swindon supermarket on Thursday.
Police have been granted a 24-hour extension to question the suspect.
Ch Supt Fulcher revealed that the man took him personally to the location of 22-year-old Miss O'Callaghan's body, in Uffington.
He was then taken to a second location near Northleach, Gloucestershire, where officers have been searching throughout the night for the second body.
Roadblocks were set up around the villages of Eastleach Turville and Eastleach Martin, as police scoured an area around a farm for clues.
Sky's midlands correspondent, David Crabtree who is near Eastleach said: "Chris Halliwell brought the police here, to a specific field on Baxters farm, to a very small area.
"He (Halliwell) pointed at what was a ploughed field so today there is a digger digging quite deep trying to find out if there is a body.
"The police really do not know what they are up against until this search has reached its conclusion."
Ch Supt Fulcher said the operation was a "painstaking" one.
"It is not a simple issue to ascertain whether there is a second body at that location so we do not know what we are dealing at this stage."
He added that when Miss O'Callaghan was first reported missing, the case immediately caused him to become concerned.
"She was a lovely girl from a stable family and her not contacting her family was completely out of character," he said.
The fast-moving case has seen a number of developments in recent days.
After Miss O'Callaghan's disappearance on Saturday, police used mobile phone technology to narrow down a search area in the 4,500 acre Savernake Forest.
They then seized a green Toyota Avensis taxi they had appealed for in connection to the case, and shortly afterwards arrested a suspect.
By Thursday afternoon, a white police tent had been erected in the front garden of a house in suburban Swindon, where specialist officers carried out detailed searches.
By the end of Thursday, Miss O'Callaghan's body had been found, and officers had revealed they were also looking for a second body.
Miss O'Callaghan was last seen on CCTV leaving Suju nightclub, in Swindon's Old Town area, after an evening out with friends.
She lived in a flat just half a mile away with her boyfriend Kevin Reape, 25.
Mr Reape, a quantity surveyor, raised the alarm at 9.45am on Saturday when she had not returned to their flat.
Miss O'Callaghan's family earlier thanked members of the public who had helped in the search for their "beautiful girl".
Hundreds of people - many who did not know Miss O'Callaghan - joined police searches of Savernake Forest, near Marlborough, or put up posters appealing for help.
"We have been so touched by the support shown by the community that we wanted to express our thanks," the family said in a statement.
:: Anyone with information is asked to contact Wiltshire Police on 0845 408 7000 or Crimestoppers on 0800 555 111
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