document: Eve Stratford, 22, who worked at London's Playboy club, was found with her throat slashed in her home in Leyton, east London, in March 1975.
  Six months later, Lynne Weedon, 16, died after being attacked and raped near her home in Hounslow, west London.
  A link was made in 2006 after matching DNA was found on the victims.
  Investigating officer Detective Chief Inspector Noel McHugh said: "I firmly believe there is someone out there who has information about who carried out these murders.
  "It's inconceivable the killer of Eve and Lynne has kept the perfect secret for 40 years."
  Describing the guilt as a "heavy burden to carry", Mr McHugh appealed in particular to mental health professionals and prison officers who may have received disclosures from a patient or prisoner.
  He said that the killer "must have let details slip over the years - maybe to a partner, a friend, even a cellmate - and I would appeal to anyone with information to contact us."
  Ms Stratford, who was last seen walking home on 18 March 1975, was found dead with her hands tied by a scarf in the bedroom of her flat after her neck had been cut almost a dozen times.
  A neighbour had heard a conversation between a man and a woman coming from her flat, followed by a loud thud.
  On 3 September 1975, Lynne Weedon was hit over the head with a blunt instrument as she walked home.
  She was then thrown over a fence into the grounds of an electricity sub-station, where she was raped. She died a week later of her head injuries.
  Police have described the killer as a white male, aged between 17 and 30 in 1975.
  Now likely to be in his 60s or 70s, police say whoever killed Eve Stratford may have known her - as there was no sign of forced entry into her flat.
  The killer also would have had a clear link to both the Leyton and Hounslow areas, according to police.
  Eve's father, her last living relative, has since died without finding out who killed her or why.
  Lynne's parents, now both in their 80s, said they are still waiting for answers.
  Her mother, Margaret Weedon, described the murder as a "true life sentence" for the family.
  Making a "mother's plea" for anyone with information to come forward, she said: "We have missed out on so much; she missed out on life, no relationship or marriage, no career or children or even just travelling the world, all taken from her.
  "We are left 40 years on always wondering what it would have been like.
  "We are well aware that whoever murdered Lynne also murdered Eve Stratford. That young lady also had her life snubbed out. Her family have died now."
  Mrs Weedon said the pain of her daughter's death still sits "deep somewhere inside".
  She added: "There are so many questions. So many thoughts. So much heartache.
  "Please, please give us some sort of closure."
summary: The Metropolitan Police has offered a £40,000 reward for information on the linked murders of a bunny girl and a teenager.