She stood on the threshold of an acclaimed career as a marine biologist.

A high achiever with three A-levels and ten O-levels, Joan Lesley McMurray had easily gained entry to Southampton University where she was regarded as a popular and hard-working student.

Her final exams in the three-year course were a few days away, and to alleviate the worry and simply because she wanted exercise, she said good-bye to her boyfriend and other pals for a solitary stroll from Shawford along the Itchen Navigational Canal towpath to reach her room at Montefiore House, the university's halls of residence in Portswood.

Near Bishopstoke recreation ground, she stopped and chatted to labourer Peter Presland about fish and birds for several minutes before resuming her walk.

Lesley McMurrayLesley McMurray (Image: Echo)

Then she vanished - and so began one of the most baffling mysteries to face Hampshire police.

Somewhere, the eldest of three close sisters was ambushed and her body dumped on a railway embankment about three-quarters of a mile from her intended route.

Read more: Who killed Teddy Haskell? An Edwardian murder mystery

Only one person knows the answer to what happened on that sunlit Spring day - the killer. He has never been brought to justice but detectives are sure of his identity.  He is safely secured in a top psychiatric hospital and will never be released.

It was shortly after noon on June 2, 1969, that 21-year-old Joan set off on her walk.

When her boyfriend went to see her two days later, he realised she had not returned to her room and contacted the police who scoured footpaths by the Itchen. It was initially feared she had fallen into the canal and a specialist team of Royal Navy frogmen were brought in to search its deep sluices and locks, but all in vain.

Det. Insp. John Baker, who led the investigation, scoured the scene by helicopter, and Echo publicity brought several phone calls from the public, confirming they had seen the 5ft 8in tall Joan, who at the time had been wearing maroon corduroy jeans, a dark blue crew-neck sweater and a coloured raincoat, in the Bishopstoke area. She had also been carrying an expensive off-white, foreign-made handbag.

Her heartbroken parents, who had flown back to England from Bahrain, were kept fully informed of the search as they waited in hope and for news. 

Her father, an electrical and mechanical senior engineer with the Ministry of Public Buildings and Works, clung to the desperate hope Joan had been badly injured or was suffering from a form of amnesia and unable to summon help, but her mother knew otherwise. Joan was dead and she desperately wanted her daughter's body to be found. 

"I simply must know," she told the Echo. "I have thought of every possible explanation for her disappearance, but in my heart, I feel she is no longer in this world. Lesley was such a gentle and loving girl. She loved us and she loved home. It is simply not in her character to have left her us for so long without a word. Something must have happened to her."

Then, on June 27, the hunt was switched to the Bench beauty spot at Lyndhurst where her clothing was found neatly folded, and armed with sticks, spades and tracker dogs, police scoured the locality, but the discovery proved to be a devious trick conceived by the killer to lure them away from the original search area.

But that was revived nine months later when her corpse was finally discovered by a dog walker near the Southampton - Winchester railway track. It was however was so badly decomposed it was impossible to determine the cause of death and in the circumstances the County Coroner Harry Roe could only record an open verdict.

Joan's funeral service was conducted in a private chapel in Winchester. The brilliant student, who was awarded her BSc "in abstensia," was mourned by about a dozen people, consisting of her parents, six close relatives, her roommate at the halls of residence, a university representative and Baker who kept in touch with her family during and after his distinguished police career. 

READ MORE: A terrible case of manslaughter

Following the service conducted informally and without music by her uncle, a Free Church minister, she was laid to rest at Magdelan Cemetery outside Winchester. Her grave, surrounded by several wreaths, was inscribed 'Always loved and remembered.'

In an exclusive interview with the Echo in 1995, the now retired Baker revealed that apart from the identification, there was nothing forensically to assist them. "It is impossible to say how she met her death. But of one thing, we were sure - there was no way she would have been walking there on her own accord. It was three quarters of a mile from the path and she was lying on railway property, on an embankment that was fenced off. Only one man knows what happened - the man who killed her."

He believed sex was the motive, a rape attempt that went horribly wrong, and she died trying to fend him off. Though she was tall, she was slim, weighing - he thought - about eight stone, and the killer carried her corpse from the death scene to the spot where she was dumped. "This could have been achieved by a healthy young man."

Several people with convictions for sex offences were questioned but one by one they were eliminated. "It's very much a personal view but I'm sure the killer was a local man. It was committed in an area which would not have been known to a passing motorist or lorry driver. Only someone with a detailed knowledge of the area could have done it because the body had been moved to a right angle to the search area. To carry the body three quarters of a mile to the railway embankment indicates the strong possibility of local knowledge."

His view was endorsed by Hampshire's top cop, Detective Chief Superintendent Cyril Holdaway, who at a press conference in 1979 to mark his imminent retirement, indicated the wanted man was already in prison. "I do not think we need to look for anyone else at all. I think we know who he is and that person will never again be a danger to the public." 

And their belief the killer was a local man came with a dramatic development on December 16, 1999, when police announced a man had been summoned to appear before magistrates in Worksop, Nottinghamshire, following an interview with a patient at Rampton Hospital. He was named as Malcolm Fletcher, 51, who at the time of the murder had been working as a sewage plant worker at Eastleigh.

However, when the case reached Nottingham Crown Court, the case was dismissed on legal grounds. Of the decision not to offer evidence, the Crown Prosecution Service explained: "It is clear from the outset of the prosecution there would be difficulties in presenting the case due to the passage of time that has elapsed after Miss McMurray's death."

In a statement, Joan's two sisters paid tribute to the sterling work of Hampshire police. "Sadly, despite their dedication and most thorough investigation, judgement on the legal process and case evidence has caused an acquittal but this investigation has filled in most of the unknown facts concerning her death."

Hampshire MP Gerald Howarth, who had dated Joan for a year after meeting her at a student ball, said: "She was just a very, very lovely girl, well- mannered but with good fun, a well-balanced, well-rounded girl, sensitive and charming."

Also paying tribute to the police's efforts, he said: "All Lesley's friends are extremely grateful for the tremendous effort they have put in over the last 18 months. It has been a heroic effort going back 30 years. Obviously, we are disappointed the murder charge has been dropped and therefore, whoever was responsible for Lesley's murder will not be brought to justice.

READ MORE: SS Hilda and Southampton's forgotten and harrowing tragedy

"However, I understand the police have deemed it appropriate in all their investigations to close the file and believe this in itself gives an indication of how things stand."

At the same hearing, Fletcher admitted four unrelated sex offences and was ordered to remain at Rampton indefinitely where he had been detained since killing and sexually assaulting a seven-year-old girl in 1973 at Eastleigh. 

Perhaps one day, the killer's troubled conscience might persuade him to talk, perhaps in a deathbed confession, which will ultimately solve the mystery and explain the exact circumstances how and why Joan died.

Until then, the police file is officially marked 'Closed.'