A tag attached to the keys bears the code 'T144213'
A set of three Ford car keys was discovered very near to the body of a murdered Wiltshire woman, whose remains were discovered beside the M5.
Melanie Hall, 25, went missing after a night out in Bath on 9 June, 1996.
Detectives on BBC's Crimewatch revealed the set of two ignition and one red "programming" key date to the 1990s.
Black bin bags containing Ms Hall's bones were found by a workman at the side of the M5 motorway near Thornbury in South Gloucestershire, on 5 October.
Det Supt Mike Courtiour said: "We really need to know what vehicle these keys relate to and what connection is there to Melanie?"
It was also revealed the reward for information leading to the arrest and conviction of Ms Hall's killer has now increased to £20,000.