Detectives investigating the suspected murder of a sailor who disappeared in Gibraltar are to appeal on television to a person with vital information.
Simon Parkes was last seen in Gibraltar in December 1986
Simon Parkes was 18 when he disappeared after a shore trip from the aircraft carrier HMS Illustrious in 1986.
The South Gloucestershire radio operator's body has never been found.
Hampshire police will appeal to a person who contacted the BBC after watching BBC Two's July documentary, Body Hunt: The Search for Simon Parkes.
'Unanswered questions '
Det Insp John Ashworth, who has been leading the investigation, said: "I would strongly urge this person to contact us.
"I have always been convinced that someone out there knows what happened to Simon.
"This inquiry has been running for a long time now, and his family need to have answers to their questions.
"For his family's sake, I would appeal to the person who called the BBC in July, to please get in touch."
Mr Parkes went missing after a night out with his colleagues.
Officers from the Royal Gibraltar Police have been involved in a joint investigation with Hampshire Constabulary into his disappearance since 2000.
The appeal will be made on Crimewatch at 2100 BST on BBC One.