Detectives investigating the murder of university graduate Melanie Hall nearly 20 years ago have made a new appeal for information.
On BBC Crimewatch, Avon and Somerset Police revealed they want to talk to anyone who owned or knew of a particular white VW Golf GTi hardtop during the summer of 1996.
They believe the owner of the car, with the registration C752 CYE, may have vital information that could help the inquiry into the 25-year-old's murder.
Miss Hall, who worked at the Royal United Hospital in Bath, vanished after a night out at Cadillacs nightclub in Walcot Street, Bath, in June 1996.
In 2009 her remains were found by the side of the M5 by a workman who was clearing vegetation on the slip road at junction 14, near Thornbury, south Gloucestershire.
Detectives said they wanted information about the car, which they believe has links to Cardiff and the Pentwyn area of the Welsh capital, from the beginning of April 1996 to August 7 1996.
During that period the Golf was not registered with the DVLA, police said.
Detective Superintendent Mike Courtiour, who is leading the hunt to bring Miss Hall's killer to justice, said: "We are very interested in this car and its possible connection to Melanie's disappearance, and we are appealing for anyone with knowledge of it to contact us, even after all these years."
Last October - on the fourth anniversary of the discovery of Miss Hall's body - detectives said they had found another white VW Golf GTi, a soft-top cabriolet, which they described as a "significant line of inquiry".
Officers also said they had received "significant information" about a blue rope used to tie up Miss Hall's body.
Mr Courtiour said his team was still investigating whether that car was relevant to the inquiry and are still carrying out forensic tests on some blue rope, which is similar to that used to bind her body.
"Our work into Melanie's murder remains very much active and positive. We are following up a number of leads, of which this missing Golf GTi could be very important," Mr Courtiour said.
Miss Hall's father Steve spoke last year of his hope that his daughter's killer would be brought to justice.
"Gradually the pieces of the jigsaw are being put together to bring Melanie's killer or killers to justice," he said.
"We always knew it would take a long time, but these new developments appear very encouraging.
"It's time for whoever has information about Melanie's murder to come forward and bring this to an end - because it will come to an end eventually.
"The police won't give up until they get a result."
A 44-year-old man, from Bath, who was arrested last year on suspicion of Miss Hall's murder remains on police bail.