One of them was brutally murdered – her headless body dumped in a field at Cockley Cley, near Swaffham – and the other, Pamela Exall, has never been found since disappearing from a campsite at Snettisham.

But despite extensive investigations into both cases, which have taken detectives the length and breadth of the country, and even overseas, each has remained unsolved since they happened on August 27, 1974.

Both cases have since been looked at by Norfolk Constabulary's cold case team, which was set up in August 2008 to investigate murders, missing people and serious sexual offences which have not been resolved and in some cases stretch right back to the 1960s.

Tony Deacon, a retired senior Norfolk detective and cold case manager, said neither the Cockley Cley case nor the Pam Exall case, like any other cold case being looked at by the team, was ever forgotten.

He said: 'There is this issue with missing people and people who have been killed, that the family suffers every day since – it creates a heartache that never leaves. We have a duty to do what we can to help these people.

'I don't think you can underestimate that point that they've suffered and that's why we should help do all we can to help bring closure for them.'

The team, based in Wymondham within the joint Norfolk and Suffolk Major Investigation Team (MIT), has used advances in forensic science, such as DNA familial profiling, to try to find new information which could help resolve each inquiry.

In December last year, the team, made up of five police staff, used the Norfolk Constabulary website to launch a new cold case section, featuring the Cockley Cley case and Pam Exall case, in the hope that the internet might prove an innovative tool to prompt fresh information.

More than 50 pieces of information have come in to the team, although not yet anything that could take any of them forward.

Mr Deacon said: 'We're in a very knowledgeable position about each case, having found all the paperwork and carried out further inquiries to close the gaps that arose from the original investigations. Although we haven't brought it to a successful conclusion, the gaps have enabled us to focus on anything that comes in in the future.'

But speaking on the anniversary of two of the county's unsolved cold cases, Mr Deacon reiterated the plea for anyone who might know anything about either case – or any other featured on the website, to come forward. He said: 'If there are people out there who know about these cases or any others, we're here to listen. The website is there all the time; there's email, and Crimestoppers. Any approach to the police doesn't have to be direct, it can be indirect. The key thing is that these cases are never forgotten.'

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