The taxi driver who received a life sentence for the murder of Sian O'Callaghan had a second murder charge dropped following a serious police blunder.
Christopher Halliwell, 48, admitted to killing 22-year-old O'Callaghan at Bristol Crown Court and must serve a minimum of 25 years in jail.
It can now be revealed Halliwell also admitted to killing Becky Godden-Edwards, 28, and even showed police where he buried the body.
A High Court judge revealed the second murder charge against him was withdrawn after the officer involved breached his human rights by ignoring arrest guidelines.
The father-of-three Halliwell confessed to Det Supt Steve Fulcher to killing O'Callaghan and showed him where he had buried the body near the Uffington White Horse in Oxfordshire.
Then in a stunning development, the former bin man, turned to the officer and said: "Do you want another one?".
Halliwell then took Fulcher to where he buried Godden-Edwards, who had been missing since 2003, at Eastleach in Gloucestershire.
The confessions came during a three hour private interview between Fulcher and Halliwell which took place at remote Barbury Castle in Wiltshire - where police suspected O'Callaghan might be - instead of a formal interview at a police station.
He was subsequently charged with both murders, but within weeks his lawyers had applied to have both cases thrown out on the grounds that DS Fulcher had not followed the rules regarding questioning a suspect.
The judge in the case Mrs Justice Cox ruled that all the evidence related to Halliwell's confessions and the discovery of the bodies was inadmissible.
Fortunately police had enough forensic evidence linking Halliwell to Miss O'Callaghan's death to charge him with murder and he pleaded guilty.
Fulcher defended his actions as he thought there was still a chance he could save O'Callaghan.
Appearing at Bristol Crown Court earlier this year Fulcher said: "I did think it was utterly ridiculous that someone who took me, 12 people and a surveillance helicopter to the deposition sites of two bodies would then seek to find some loophole or quirk in the law to get away from the fact that he was a multiple murderer.
"It was my responsibility as the SIO (Senior Investigating Officer) responsible for Sian, for her life or her death. The last thing I could do is speak to him in person and that's what I did.
"The sole purpose was to seek to appeal to him to show me where Sian was with the intention of saving her life."
Mrs Justice Cox ruled Fulcher breached Halliwell's rights by failing to caution him with regards the second murder and refusing to give him a solicitor once he made the confession.
The judge added: "As soon as he began to talk about another offence it is clear that he should have been cautioned."
Fulcher admitted that he did not caution Halliwell or offer him a solicitor - breaking the Police and Criminal Evidence Act (PACE).
Fulcher has now been suspended by Wiltshire Police for breaching arrested guidelines and an investigation is pending by the Independent Police Complaints Commission into allegations of "inappropriate contact with the media".
The family of Godden-Edwards said they do not blame Fulcher for what happened.
Mer mother told the Daily Telegraph: "Steve Fulcher is a committed and dedicated police officer and a family man. As far as I am concerned he is a hero and I just want to give him a big hug.
"He knew that if he took Halliwell back to the police station and allowed him to see a lawyer, any chance of him owning up to what he had done would be gone. We would probably have never found Sian and I would still not know where my daughter was.
"He has lost his job for doing his job and it is an absolute disgrace."