Ben KendallTime is running out in the bid to solve a 40-year-old murder mystery, cold case detectives said as they mark the anniversary of the killing.Officers investigating Susan Long's death in 1970 remain hopeful that breakthroughs in forensic science could hold the key, but the passage of time means both the attacker and vital witnesses will now be in old age.Ben Kendall

Time is running out in the bid to solve a 40-year-old murder mystery, cold case detectives said as they mark the anniversary of the killing.

Officers investigating Susan Long's death in 1970 remain hopeful that breakthroughs in forensic science could hold the key, but the passage of time means both the attacker and vital witnesses will now be in old age.

The 18-year-old Norwich Union worker had taken the bus home after visiting her boyfriend in Norwich and her parents grew concerned when she did not return.

She was found dead in a lovers' lane less than a mile from her home in Aylsham and, despite exhaustive investigations, the killer was never found.

Det Insp Andy Guy, who heads Norfolk police's cold case team, said the 40-year anniversary could represent the last chance to crack the case.

'The case will never be closed until we have caught the person responsible but we have to be realistic and accept that as time passes our chances of finding new information decrease rapidly,' he said.

During the inquiry police recovered the attacker's blood from Miss Long's body and, unusually for a case of that era, they have a full DNA profile of the suspect.

Advances in familial DNA testing mean the killer could be traced if any of his relatives were arrested for an unrelated crime. Alternatively, the technology could be used to identify the killer even if he was already dead.

Det Insp Guy said the answer may lie in a death bed confession or in a rumour previously dismissed as too ridiculous to be true.

He said: 'During the original investigation it became clear that Susan would never have got into a car with somebody she didn't know unless they were in a position of authority.

'This is a line of inquiry which has persisted over the years. It may be somebody heard a rumour about a local community leader or somebody in a position of responsibility and dismissed it as being out of the question. But there is a chance those rumours could hold substance and lead us to the killer.'

Miss Long's widowed mother, Molly Long, 84, did not want to speak as she marked the anniversary in private. Det Insp Guy said she had learnt to manage her grief and discussing the crime would bring back painful memories.

He added: 'In cases like this we are dealing with families who have lived with their grief for decades and this is added to by the uncertainty of not knowing what happened to their loved one.

'They have to learn to live with that but we cannot give up hope and, while there is any prospect of finding justice, we have to continue searching for answers.'

Anyone with information which could be relevant to this investigation should contact Norfolk's cold case team on 01953 424548.

Do you have a crime story for the Evening News? Contact crime correspondent Ben Kendall on 01603 772423 or email ben.kendall@archant.co.uk