Fifty years on from the murder that shocked and captivated the world, the Crown's case against Lord Lucan was exclusively revealed in the Mail, with extracts from a 60-page confidential report outlining in gripping detail the evidence that Scotland Yard had compiled against him.
Written in early 1975, in the run-up to an inquest in June that year, it gives a definitive account of the murder of the Lucan family nanny, Sandra Rivett, and the attempted murder of Lucan's estranged wife Veronica.
Today our coverage of the infamous crime continues, with a focus on the 'forgotten victim', murdered nanny Sandra Rivett.
Every year, as the anniversary approaches, the familiar feelings of grief, emptiness, anger and bitterness begin to stir in the mind of Dawn Roberts. This year it will be even more intense.
Sandra Rivett, then 29,was bludgeoned to death with a piece of piping in the basem*nt of a house in London 's Belgravia, her body bundled into a mail sack and left in a pool of blood
She was estranged from her husband Roger, pictured, at the time of her death
Sandra, holding a distinctive broom, is said to have shown an interest in witchcraft
For it is 50 years since the terrible night of November 7, 1974, when her sister - whom she adored and looked up to - was bludgeoned to death with a piece of piping in the basem*nt of a house in the wealthy enclave of London's Belgravia, her body bundled into a mail sack and left in a pool of blood.
Sandra Rivett, then 29, was nanny to the Lucan family. And the perpetrator? The prime suspect to this day is the 7th Earl of Lucan, who vanished without trace in the hours after the killing.
Speaking at her home in Hampshire this week, Dawn's tears flow readily as she recalls the tragedy and its impact on the family - their parents and two other sisters. It is clear that, half a century on, she has still not come to terms with it.
For her, the sense of loss is ongoing. She is haunted by reflections on how Sandra's life might have turned out. Added to this is the fact that not only has she lost a relative to murder, she has not yet gained justice for her.
Lord Lucan's AA membership card, which he left behind before driving off and disappearing
In the aftermath of the bloody events at 46 Lower Belgrave St, there was intense worldwide interest in the aristocratic Lucan family, and their friends in the 'international socialite set' - many of them wealthy and powerful, who moved swiftly to protect Lord Lucan.
'No one paid for her murder': Grief of sons tormented by their mother's brutal death
According to DCS Roy Ranson's report, Sandra Rivett (nee Hensby), gave birth to a son in March 1964 when she was 18. The father was a John Andrews whom she'd met while she was a voluntary patient at Redhill Mental Hospital in Surrey where she was treated for depression.
Her parents, Albert and Eunice, legally adopted the child, called Stephen, and he was brought up believing that his mother was in fact his sister - a not uncommon arrangement in those days.
At the time of her death, Stephen Hensby was ten and it would be some years later before he realised that Sandra was his mother.
In an interview with the Mail in 1999, marking the 25th anniversary of her brutal killing, he said: 'I keep thinking that no one has paid for my mother's murder, no one has been caught and incarcerated for it,' he said. 'My grandparents went to their graves still grieving that her killer had got away and that no one had been punished for taking her from them.'
He declined to comment ahead of the 50th anniversary.
Sandra Rivett had another son in 1967, who was given up for adoption. Neil Berriman, a 57-year-old-builder had no idea who his biological mother was until years after his adoptive mother Audrey died, leaving him a letter which provided clues to her identity.
He has been very open about the torment he has suffered from belatedly learning that his birth mother was the victim of one of Britain's most enduring murder mysteries.
Currently working on a TV documentary series about his mother's murder, he has his own theories about the case and more recently became convinced that an elderly British Buddhist living in Brisbane, Australia is Lucan, although Scotland Yard has dismissed the theory.
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But there was little or no interest in Sandra who, down the years, has become the 'forgotten victim' in the Lucan mystery. She was only ever 'the nanny', says Dawn.
Mrs Rivett - she was estranged from her husband Roger at the time of her death - was not the intended victim, detectives believe. Indeed, she shouldn't even have been in the house that night: it was her usual day off, but a sore throat meant she decided to swap days.
According to police, the person Lord Lucan wanted to kill was his estranged wife Veronica, with whom he had been in a bitter custody battle over their three young children who were upstairs in their bedrooms in the five-storey house that night. Lady Lucan, too, was bludgeoned and suffered serious head injuries, but managed to escape and raise the alarm.
Now 71, Dawn says: 'Sandra was my older sister - eight years older. Her death left a massive gap in our family. She looked after me. She would have helped me after I had [my] baby had she been there.'
In November 1974, Dawn's husband was in hospital and she was coping on her own with a new baby.
'I think that's why I was never able to process her death properly at the time,' she says sadly. 'I think I am only just processing it now.'
The milestone anniversary of Sandra's death – or, for some, Lord Lucan's disappearance – has renewed focus on the most enduring mystery of this infamous crime.
Today, the Mail published a never-before-seen Scotland Yard report from 1975 which, over 60 pages, gives the definitive account of events before, during and after the crime and in gripping detail spells out why police believe that Lucan - and only Lucan - was responsible for the murder of Mrs Rivett and the attempted murder of Lady Lucan.
Written by the lead investigator, Detective Chief Superintendent Roy Ranson, the document - entitled Regina V The VII Earl of Lucan Report - would have formed the basis of the Crown's case against the peer had he ever been brought to trial.
The Mail has also launched a landmark True Crime podcast series, The Trial Of Lord Lucan, in which two eminent barristers, informed by the official police document, will argue the case and call on witnesses in a week-long podcast event starting on Monday June 3. Listeners are invited to act as jurors and give their verdicts - innocent or guilty - on MailOnline.
Dawn speaks softly and wipes her eyes throughout our meeting as she describes how the Lucan tragedy has affected her life.
Who was Lord Lucan?
Richard John Bingham, the 7th Earl of Lucan, was not your archetypal murder suspect.
An Old Etonian from a well-known aristocratic family, he developed a taste for the high life after finishing National Service in 1955. He raced power boats, drove an Aston Martin and flamboyantly left his job in a merchant bank to become a professional gambler.
But as his losses mounted in the gambling clubs of Mayfair and Belgravia, the playboy peer a father-of-three found himself mired in debt and his marriage doomed.
It was against this background of deepening financial and domestic strife that the handsome 39-year-old is alleged to murdered his children's nanny Sandra Rivett, mistaking her for his estranged wife, who he also allegedly attacked on November 7, 1974 before going on the run.
The Rivett murder - at the Lucan family's home in central London came to light after Lady Lucan ran to the local pub, the Plumbers Arms, collapsed on the floor and screamed: 'He's murdered the nanny and he's after the children.' Mrs Rivett's body was found in a canvas US mailbag in the basem*nt of the five-storey house at 146 Lower Belgrave Street.
But Lucan was nowhere to be seen. Although he rang his mother later that evening, and turned up at the address of a family friend in Sussex where he had a whiskey and water and spent less than two hours - there have been no confirmed sightings of him since.
The cause of Mrs Rivett's death was 'blunt head injuries'. Police concluded that the lead piping found at the murder scene probably caused her injuries.
Lady Lucan had five lacerations of the skull and forehead. They were deep and jagged and if she had received these wounds to the rear of her head, they may have been fatal. She also had lacerations on the inside of her mouth.
By any standards, it was a brutal murder and could easily have been a double killing.
An inquest into the death of Mrs Rivett was held in 1975. In his absence, the jury returned the verdict: 'Murder by Lord Lucan.'
In the five decades since, there have been dozens of supposed sightings of him in various locations in the UK and around the world - all documented in statement form and followed up by the Met. Yet Lucan has never been found and still remains wanted for murder.
Officially the case remains 'open', but plans for a full-scale new investigation were blocked in 2004 by senior Yard commanders, who questioned what it would achieve and at what cost. If still alive, he would be 89.
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'I've never been able to talk about my sister's murder. I was given parts of the [recent] Amazon documentary to watch – the parts involving my sister – to make sure they were accurate, and it's brought Sandra back to me.
'I didn't watch it all. They didn't give me the horrible parts to watch. I know what happened, but I don't want to see it.
'At the time, nothing much was said in the newspapers about Sandra. It was all Lord Lucan and his rich friends and then it was 'the nanny'. She was only ever 'the nanny'.'
During the inquest into Sandra's death in June 1975, her family complained about how the case was being conducted, with Press and police seemingly more concerned with the personalities and antics of the Lucan family and their friends than with the brutal murder of an innocent young woman.
Mrs Rivett's father, hospital worker Albert Hensby, then 60, told the Mail at the time: 'My daughter's name has hardly been mentioned. Yet she is the reason why we are all here. She was a kind, gentle person who loved children and wouldn't hurt anyone.'
Aware of a plot by Lucan's friends to smear Sandra Rivett by suggesting she was promiscuous and had been murdered by an angry lover, the Scotland Yard document reveals that police delved deeply into her background to establish her character. They interviewed her estranged husband and identified former boyfriends through her diary and an address book - all of whom had alibis.
One of the men named in the report revealed to the Mail this week that police had quizzed him about Sandra Rivett's alleged interest in witchcraft.
References to her attending black magic meetings in south London were found in her diary, according to the man, now 76, who asked not to be named.
Speaking for the first time, he said he met Sandra in 1972 but had lost contact with her more than a year before she was killed.
'I only found out she'd died from the papers. The headline read: Nanny Murdered. I saw her name, Sandra Rivett, and I couldn't believe my eyes. I had to read it several times.
'I didn't know she worked for Lord Lucan. I didn't even know where she was. She liked the peace and quiet, so it was quite amazing she was in London.
'My first impressions of her were that she was a nice girl, slim and pretty. She was a smart dresser. She was not posh, but she spoke properly. She had a normal London accent.'
He said two CID officers had visited him and asked him about Sandra's supposed interest in black magic. 'They asked me 'Do you know she was into witchcraft?' I said 'No'. There was nothing strange about her house.
'Apparently she used to go to a witchcraft club somewhere. Apparently they used to have meetings. This is what the police told me. I didn't know there was a witchcraft club.'
He added: 'Her murder was a shame. It's a sad thing, to be bludgeoned to death like that. Lord Lucan is a bloody psycho. She was a nice person. She would not hurt a fly.'
Dawn does not believe, as many do, that Lucan killed himself and is angry with those who may have helped him evade justice.
'His rich friends helped get him out of the country,' she says adamantly.
She harbours no anger towards the police for not solving the murder and says they showed her family kindness.
'The police saw my parents a couple of times afterwards. They were very good to them. It was all very nice... But then that was it. They left us alone. There was no after-care.'
Today Dawn is resigned to the fact that her beloved sister's murder will never be solved.
Of Lucan, she says simply: 'I would like to see his bones. Though, knowing him, he's probably still alive.'
- Special reporting by Stephanie Condron.
NOW LISTEN TO THE TRIAL OF THE LORD LUCAN PODCAST
In a world-exclusive true crime podcast event, The Mail brings you The Trial Of Lord Lucan.
Inepisodes released daily from Monday 3 June to Friday 7 June, two real-life eminent barristers will argue whether Lord Lucan was innocent or guilty using the bombshell new document and unheard-of evidence in an unmissable twist on courtroom drama.
Follow the highs and lows of the case in forensic detail in the podcast, and then on Friday 7 we'll ask YOU to act as a jury here on Mail Online in a fascinating public vote.
So will you clear Lucan... or not? Listen to the podcast and decide for yourself.
Listen to The Trial Of Lord Lucan everywhere you usually get your podcasts.
