Detectives investigating the murder of estate agent Suzy Lamplugh could use new forensic techniques to examine a DNA sample found in her car.
The sample is likely to be looked at when police decide to hold a forensic review of the case.
Ahead of the 20th anniversary of Miss Lamplugh's disappearance on July 30, detectives are hoping it could eventually provide a break-through in the hunt for her killer.
They have refused to discuss the size or relevance of the DNA sample and say there are no current plans for a forensic review.
However, it is policy to periodically re-examine DNA evidence in any open investigation, especially given recent advances in technology.
Detective Superintendent Jim Dickie, who is leading the investigation, said: "I have not given up hope that a piece of vital information will come.
"I will leave no stone unturned and am committed to being able to allow the Lamplugh family to move on and reach a sense of closure."
Convicted sex killer John Cannan, from Sutton Cold-field, who has been inter-viewed twice over the case, remains a suspect.
Miss Lamplugh, aged 25, vanished in July 1986 after going to show a house in Fulham, west London, to a man calling himself Mr Kipper.
She was declared dead in 1994 but her body has never been found, despite searches in Worcestershire and in Somerset. The case was officially reopened in 2000.
Three days before she vanished Cannan was released from a hostel at Wormwood Scrubs Prison, where he had been serving a six-year sentence for rape.
Scotland Yard has been investigating Miss Lamplugh's abduction and murder for the past 20 years.
In June 2002 a file was submitted to the Crown Prosecution Service. Police were told that there was insufficient evidence for a prosecution.