I’ve worked as a criminologist for some 40 years, specialising in violent crime, so I am used to discussing, researching and trying to understand murder in all its various guises. I’ve talked with hundreds of murderers, many hundreds more who are suspected of having committed murder and, saddest of all, the families of the victims left behind.

Over the years I have come to understand the public’s fascination with murder, especially serial murder, and developed stock answers to questions I regularly get asked. Are people who commit murder born evil? Do you enter the mind of a serial killer? And, perhaps most commonly of all, how do you cope?

My various coping strategies have been honed over the years but they were tested to the limit by the murder that is the subject of my new book. The case has engrossed me for the past two years, not least because for the very first time the murder felt personal. I was returning to my home town in Lanarkshire at the request of my sisters and their friends to look again at a case which had nagged away at them for decades. What I was to discover made me profoundly uncomfortable as a brother, man, Scot and criminologist.

In July 1973 a 23-year-old woman called Margaret McLaughlin was murdered as she took a shortcut from her home in Glenburn Terrace, Carluke, through an area known locally as Colonel’s Glen to catch the 8.03pm train into Glasgow. Margaret had recently got engaged to Bob Alexander, although he was working that summer in South Africa. Margaret was going into the city to meet her soon to be sister-in-law to make plans for the wedding. She was about to start the rest of her life.

The journey from her home to the station should only have taken her a few minutes, but Margaret never emerged from the glen. Her body was found the following morning and it was obvious she had been subjected to a ferocious attack; she had been stabbed 19 times.

In an era before CCTV, mobile phones, a national DNA database or “offender profiling”, and when forensic science was still in its infancy, it didn’t seem that the Lanarkshire police and their lead detective William Muncie – “Scotland’s top detective” - would have much to go on. But within the week they had arrested and charged a 19 year-old local man called George Beattie with Margaret’s murder. Yet there was no forensic evidence to connect Beattie to Margaret’s death. He appears to have been charged as a result of his “special knowledge” of the crime scene and a pseudo-confession that he had been forced to watch Margaret being repeatedly stabbed by men who wore top hats with mirrors on them.

The jury took just 35 minutes to find Beattie guilty. All of his subsequent appeals were unsuccessful and, as far as anyone official is concerned, the case is now closed. Beattie has served his sentence and been released from prison.

In 1973 I was a teenager still living at home with my parents and two of my three sisters, Alison and Margaret; Annie, my third sister, had recently married and was living in another part of the town. Alison and Margaret still live in Carluke.

By 1975 I had gone off to university and would make my career in England. I was aware even then that my gender gave me opportunities that were denied to my sisters: their horizons were fixed at school teaching, nursing or clerical work. Those horizons were also geographically bound by Lanarkshire, while just a few years after leaving university I was living in New York, then Cambridge. This had nothing to do with talent but was merely a taken-for-granted, seemingly “natural” process that separated girls from boys and women from men. We would now call all of this prejudice.

My sisters and their friends, who all still meet regularly in a cafe in the town, wanted me to look again at Margaret’s murder and Beattie’s conviction. They are as convinced now as they were in 1973 that Muncie had arrested the wrong man. I was reluctant. What if I come to the same conclusion as Muncie? “That would be fine – we trust you,” they replied, the implication being they didn’t trust the original investigation.

Many other women in the town shared their skepticism, while most of the men – including my own father – simply accepted that Muncie and the criminal justice system had convicted the right person. The women were right to be suspicious as it became clear George Beattie had been fitted-up for a murder he did not commit.

If it was as obvious to me from documents readily available in the public domain that there had been a miscarriage of justice, why had the checks and balances of the Scottish criminal justice system not intervened to set Beattie free? Why did everyone simply go along with Lanarkshire Police’s flawed investigation that perpetuated a speedy but shoddy conviction and saw an innocent man sent to prison? I avoided these questions at the time.

Through social psychology experiments we have learned much about obedience and deference to authority. We now have a broader understanding of how and why cultures of denial exist; how people can know the truth but simply refuse to acknowledge reality.

Lanarkshire Police were jokingly known at the time as “the Masonic Lodge with truncheons” and Muncie – also a native of Carluke – was a member of the Lodge. So, too, was my father, and I began to wonder if his acceptance of the police’s version of events might have had more to do with allegiances formed in the Lodge than an understanding of the realities of the case.

Of course, if I am right about Beattie’s wrongful conviction that leaves another obvious question: who did kill Margaret McLaughlin?

As I was not engaged in a formal cold case review, I could not ask the police for the materials that would normally have been made available to me. I could, however, use the techniques I would use if I had been officially called into the investigation. For example, I could walk the crime scene, which I’d never visited before.

It soon became obvious why no one had witnessed this murder and how Margaret’s killer had disappeared afterwards without being seen. This was a murder that depended on sight lines into the glen and access to the shortcut that her killer would have taken from the back garden of one of the houses that bordered the route. I could even make a few guesses as to where her killer might have come from and returned to. Using the electoral roll I was able to put names to the men who lived in these houses and one in particular caught my attention.

I then made what turned out to be my most important discovery. During one of George Beattie’s appeals in the 1990s, Bob Beveridge, a retired detective from the Scottish Crime Squad who had been drafted in to help Lanarkshire Police with their house-to-house enquiries at the time, gave a statement to The Herald in which he stated he had interviewed the “strangest person”. He was so worried by what this young man said that he wanted him to be formally interviewed under caution.

This “strange” suspect literally “jumped off his sofa” when Beveridge entered the house, pulled up his jumper to show the detective marks on his chest, claimed he always carried a knife as he liked to stab cats, and when asked if he had killed Margaret, replied he “might have done” but couldn’t remember what he did from one day to the next. Beveridge was told to let this man go, however, as Beattie had just been charged with murder.

I tracked Beveridge down and interviewed him formally. He couldn’t remember this suspect’s name, or where he had interviewed him, but he could draw me a map. It corresponded with the houses I had identified when I walked the crime scene and I knew I could put a name to this “strangest person”.

The final part of my research was to track him down, and the 10 minutes I spent on his doorstep was probably the most nerve-jangling of my entire career. When I suggested to him that some people in the town thought he had murdered Margaret, he merely replied “I don’t know what happened” and closed the door.

I cannot prove guilt or innocence; I cannot be judge and a jury. Nor do I have access to all that I would have wanted to consider. But I have written my book in the hope that those with formal powers will want to walk in my footsteps and re-consider this case. I truly believe we are on the cusp of finally learning what really happened on the night Margaret McLaughlin was murdered. And, if Police Scotland would like me to, I am only too willing to help and make my research available to them.

The personal archaeology around this case has reminded me of a number of things, not least my love for my sisters and their friends. I also know that when I return to Carluke now I am no longer going back to the Scotland of the 1970s.

Above all, I hope the Beattie and McLaughlin families will forgive this further intrusion into their lives, that George gets justice at last and Margaret’s family can take a small measure of comfort in the fact that she has remained in Carluke’s thoughts for nearly half a century.

Signs of Murder: A Small Town in Scotland, a Miscarriage of Justice and the Search for the Truth, by David Wilson, is out now on Sphere, priced £20.