Killers who were never caught over the past 50 years are now being hunted by a new squad of detectives.

Thames Valley Police will today officially unveil a team of eight detectives put together to start trawling through the unsolved murders of the past half century and rapes in the past 27 years in Oxfordshire.

They are hoping advances in forensics and DNA analysis, changes in the law and new leads will finally lead them to catch those who slipped through the police net.

Old murder cases have previously been reviewed as a matter of routine but this is the first time a special squad, called the Dedicated Review Team, has been established.

It will be led by Det Supt Barry Halliday and principal investigator Pete Beirne, a retired Detective Chief Inspector.

The team is also hoping to 'recruit' the help of up to 900 police officers who have retired, but may have their own theories to help finally crack cases they had worked on.

Mr Halliday said: "Murders and sex offences are the types of crimes that have the most impact and the consequences are severe for all those concerned.

"The public need to have confidence that when they're told a case is never closed, it actually isn't ever closed. It's important for us to try to get some closure for surviving families and victims.

"Even if we find we can't progress a case further now, it will be reviewed again in two years' time."

The police would not reveal exactly how many cases in the county there are, but the Oxford Mail has covered at least eight murders that have not been solved over the past 30 years.

This week the Mail will review some of those cases, running features on the murders, including the case of 30-year-old Vikki Thompson, who was killed as she walked her dog in Ascott-under-Wychwood in 1995, and Janet Brown, 51, who was killed in her home in Radnage the same year.

The detectives are still working on the order of which unsolved murder they will work on first.

But Mr Halliday said: "Be under no illusions, we will be looking into those eight murders in Oxfordshire. The dedicated review team is up and running and we will be visiting families involved, but we can't give any timescales."

Family liaison officers - police specially trained to deal with families during times of trauma - will be helping families cope with having the past dredged up by the investigations.

Mr Halliday said: "We have to be very aware of the sensitivities around the work that we're doing and to make sure there are support mechanisms in place.

"We can't say to families we're going to see them next week or next month, but we will be contacting them.

Mr Halliday and Mr Beirne could not reveal how many unsolved sex cases there were, but Mr Halliday said: "We're going back as far as 1980, but it may well go even further than that."

CASE STUDY: A true mystery murder was the killing of Eila Karjalainen, whose decomposed body was found in Kings Wood, on the Duke of Marlborough's Blenheim estate in November 1983.

The 23-year-old had been strangled, her body dumped and undiscovered in the woods for up to three months. Police think she was picked up while hitchhiking and the failure to catch her killer was a great frustration for the murder team.

Her rucksack and some belongings, including her passport, were found in an A40 layby near Witney, three weeks after her body was discovered.

The case was used as the basis of one of the plots in the Inspector Morse ITV series.

Her file was re-opened in 1987 by detectives searching the killer of 17-year-old Rachel Partridge, who was murdered after trying to hitch a lift to her home at Shaw's Field Farm, Chinnor Hill.

No link between the two killings was proved and in 1989 Ronald Cheshire was convicted of Rachel's murder at Reading Crown Court.

Even then, forensic science was advancing quickly.

At the time, Det Sgt Henry Wymbs told the Oxford Mail: "Murder is the most serious crime. All the resources are immediately put in - but most are solved quickly.

"If there are no leads and the enquiries show all the suspects have been eliminated, there's no point keeping people on it for the sake of it.

"We store all the information on a computer, which can be updated at any time - even in 20 years.

"If a similar type of crime is committed in another police area, we can liaise with them with a view to tying it up."

In 2000 fingerprints were thought to have been found on the rucksack, diary and travel documents of Miss Karjalainen.

The prints were being compared with a national database. Police said that one of the mysteries of the case was that Miss Karjalainen had met a lot of people in London and written their details in the diary.

When detectives looked at the diary, pages were torn out.

The Mail's then crime reporter David Duffy, who is now deputy editor of the Oxford Times, covered the case.

He said: "The police were stuck from the start because there was a body buried and decomposed and forensic evidence was very limited.

"Police suggested whoever put the body there was local. She had visited London and then her body was found in Oxfordshire and they never filled the gap of what happened to her.

"She was dumped in the woods and you would have had to know the place was there to have found it.

"The suggestion was she was picked up in London by the person who killed her.

"Police did everything they could, there were all the usual appeals for information and it was deeply frustrating."