Video report by ITV News West of England Correspondent Rupert Evelyn
Police are investigating "new lines of inquiry" after receiving phone calls about double killer Christopher Halliwell.
The taxi driver is serving a whole life term for the murders of Becky Godden and Sian O'Callaghan - but police fear there may be more victims.
After confessing to killing Miss O'Callaghan, 22, in 2011, he took police to her body before offering to show them where "another one" was buried.
Detectives then found the body of sex worker Miss Godden, who went missing in 2003 aged 20.
Halliwell smirked as he was convicted of murdering Miss Godden at Bristol Crown Court on Monday.
And the 52-year-old - who was already behind bars for killing Miss O'Callaghan - said "thank you" as a judge told him he would never be released.
But Miss Godden's family - who almost didn't get their day in court after police failings - said justice should have come six years ago.
Becky's dad John Godden said: "Someone's got to be held accountable."
Halliwell's confessed to killing Miss Godden in 2008 and told police: "I'm a sick f*****. Normal people don't go around killing each other."
But it was ruled inadmissable in court as Detective Superintendent Steve Fulcher breached police guidelines by failing to caution and offer him a solicitor when he was arrested.
The detective resigned from Wiltshire Police in May 2014 after being found guilty of gross misconduct.
Miss Godden's mother Karen Edwards has since campaigned for changes to the Police and Criminal Evidence Act (Pace) following the case.
But after Halliwell was found guilty she publicly thanked Mr Fulcher for "bringing my little girl home".
The court heard Becky had battled with drug addiction and moved away as she didn't want to hurt her family anymore.
Although her parents didn't hear from her, they thought she was living in Bristol.
In a victim impact statement, her mum said: "I should have known something was seriously wrong when that first Mother's Day went by without a word from Becky.
"I did not imagine a funeral would replace her wedding day...I envy other mothers.
"Please don't tell me I will get over this because I never will...I have a life sentence."
In another statement, Becky's father John Godden said her death had "killed him as a father".
He added: "At times I've not been in the right place...Becky will always be with me."