Yet all along, sitting in the files, was a confession made by a 17-year-old boy just 14 months after Cheryl disappeared. The youth told the police in horrific detail how he snatched Cheryl and ran off, intending to sexually assault her. But when she cried out he tied a handkerchief over her face with shoelaces then strangled her, covering her body in leaves and dirt. The teen who made that confession – referred to in the files by his alias Mercury because he was a minor – is now in his 70s.

When the confession came to light he was charged and held in custody but when the case reached court in 2019, it was ruled inadmissible on a technicality. The charges were dropped.

To say that Ricki and his brothers, Paul and Stephen, were angry is an understatement.

The trio are now in their 60s. The trauma of their sister’s disappearance has corroded all their lives but a decision last month by the Office of the Director of Public Prosecutions to review the decision to drop the charges has offered a glimmer of hope.

For Ricki, 64, the possibility of reopening the case can never take away the sadness but it might mean he and his siblings can uphold a promise they made to their mother Carole on her deathbed in 2011 that they would never stop seeking answers to what happened to their sister.

‘We could have lived a different life if, back in 1971, police had just done their job,’ he says from the Philippines where he lives with his partner Kimberly.

Sadly Ricki, who ran a successful cleaning business before his recent retirement, is estranged from three of his four children but he keeps his Facebook open in the hope they may one day reconnect.

His Brisbane-based brother Paul, who is 60 and has raised five daughters barely letting them out of his sight, is still haunted by his sister’s disappearance.

‘When we go out I enjoy myself to a certain extent but I’m too busy checking that all my daughters and grandkids are there, making sure everyone is safe.’ His wife Linda reveals their daughters were never allowed to go to sleepovers.

In their lengthy conversations with the Daily Mail, you sense the three brothers are making up for all the years they weren’t allowed to mention their sister’s name.

Suffering in an era without counselling or support, the Grimmer family contracted into silence – but the grief seeped out in other ways. As Ricki explains, his parents had vicious arguments and, as the eldest, he was subjected to regular beatings by his father who, in an awful twist, turned out not to be his father after all.

‘He blamed me every day. I was thrown across rooms, thrown through windows, beaten all the time and I didn’t realise why there was so much hatred from him towards me, his eldest son.’

To understand how the family imploded we need to go back to January 12, 1970, when Cheryl disappeared. It was Ricki who had begged his mum to take him and his siblings to Fairy Meadow Beach, an hour south of Sydney.

The children had swum and played happily on the sand until the wind got up and Carole asked Ricki to take Stephen, five, Paul, four, and Cheryl up to the shower block to wash off the sand.

‘Because Cheryl was so young I took her into the boys’ changing rooms to get her showered off. When we came out Cheryl wanted a drink so I lifted her up to the water fountain. My brothers were running up and down and then Cheryl snuck into the ladies’ changing room.

‘I said to her, ‘come on, let’s go back, we’re going to get into trouble’ but she wouldn’t come out. She was three years old and she was smiling and laughing at me. I wouldn’t go in and instead made the fatal mistake to go back to the beach to get my mother,’ explains Ricki, replaying the scene that has tormented him ever since.

Carole returned with her sons to the changing rooms but Cheryl wasn’t there. ‘My mum was looking around and couldn’t see her and then she came up to me and shook the living bejesus out of me saying, ‘where did you leave her?’ That’s when the panic set in and she started screaming,’ says Ricki.

The police were alerted and within hours hundreds of locals were combing the beach and bushland for the little girl. The children’s father, stationed with the army in Sydney, returned home and the next day hopes were raised when police received a ransom note demanding $10,000 for Cheryl’s safe return.

Analysis of the handwriting suggested it was most likely written by a teenager but no one appeared at the handover location and police dismissed it as a hoax.

As the hours of waiting turned into days, then weeks, Vince would go out drinking, returning home to scream at Carole: ‘Why did he leave her?’ As Ricki says: ‘It changed the dynamics of our family. We were a normal family who’d come to Australia for a better life and less than 18 months later, we’re ripped apart. It deteriorated from there and kept getting worse and worse.’

As the years passed with no answers, Cheryl’s disappearance was a constantly weeping wound. Paul recalls his mother going to the newsagent on an anniversary of his sister’s disappearance and becoming distressed at the sight of Cheryl’s picture on the front page.

As he says: ‘The lady in the shop had to call us to come and get Mum because she broke down.’ Middle brother Stephen, 62, who stayed in the area for 30 years, said the memories never left him.

‘I used to do surf carnivals at Fairy Meadow Beach and you sort of have mental issues when you’re standing there or riding your bike past the beach. When people I worked with asked about it, I’d get choked up and have to walk away.’

One day when he was 13, Ricki recalls his parents fighting and he sided with his father. ‘It wasn’t long before we were due to go back to the UK because our family was a massive basket case.

‘They were arguing and I said, ‘Mum, come on, Dad’s right, stop shouting at one another’. He screamed at her: ‘There you go – and he’s not even my son’.’

Ricki says his mother threw a carving knife at his father, narrowly missing him. Ricki ran away for five days but returned home cold and hungry.

It turns out Carole had had her eldest son with another man back in Bristol, but Vince had brought up Ricki as his own.

‘I know who my biological father is but he won’t accept it and the irony of all this is that I have another half-sister,’ says Ricki. ‘I offered to do a DNA test but she doesn’t want to know.

‘It’s a bitter pill to swallow that I lost my sister and then I’ve got another half-sister who doesn’t even want to know me.’

Fortunately, he and Vince mended their relationship before his death in 2004.

While the family returned briefly to the West Country in the mid 70s, they found no peace and went back to Australia.

Ricki, who had taken his mother’s maiden name as his surname, wanted to stay in the UK so he enlisted in the Army but with The Troubles in Ireland, Carole was determined not to lose another child. She begged him to return to Australia, so he did.

Three marriages and four children later, he says he’s a good dad but was a poor husband due to the demons in his head. Once he met a woman claiming to be Cheryl but he knew instantly on meeting her that she wasn’t.

Within hours of Cheryl’s disappearance hundreds of locals were combing the beach and bushland for the little girl (Pictured on January 13, 1970)

Carole Grimmer, pictured with her sons, went to her grave never knowing what happened to her daughter, Cheryl

After his third marriage ended in 2012, Ricki says he was suicidal. ‘I was a mess. I’d had enough and a friend of my wife’s found me sitting in a car park gutter. She and her husband took me home. They probably saved my life.’

Therapy, which includes writing to his sister, has helped as has four pilgrimages along the Camino de Santiago in Spain where he has laid stones in his sister’s memory.

As he says, he feels as if he lost his sister twice: the first time when she disappeared, the second in 2016 when a detective called to tell him they’d started reinvestigating the case and had unearthed Mercury’s confession of murder.

‘That was the first time I’d ever heard the word murder. I’d always lived with the hope that Cheryl would knock on the door one day and come walking in,’ he says.

It turns out that Mercury, who had also gone to Australia from Britain, was a troubled youth and had been at Fairy Meadow Beach on January 12, 1970.

His confession is chilling. He tells how he saw the little girl with her brothers and how one of them lifted her up to get a drink.

When she came out of the changing rooms and began following her brothers, Mercury grabbed her, putting a hand over her mouth to stop her screaming because there was a ‘bloke’ sitting on the wall nearby. Having taken her to a secluded area, he put his hands around her throat.

‘I guess I must have strangled her,’ he says in the confession.

He went on to say that he considered taking her swimsuit home but decided not to. ‘I thought my mother might find it, so I burnt it in an incinerator on the beach,’ he told detectives.

Although police took the teenager to the place he left Cheryl’s body, nothing was found and they opted not to charge him.

Decades later, when the confession was unearthed, Mercury spent two years in prison awaiting trial for murder.

He pleaded not guilty and, in a pre-trial hearing, the case fell apart after the judge ruled the confession inadmissible because a caution had been issued as soon as the teenager started making admissions and not before – and because of the ‘particular vulnerability’ of the accused.

Angry and frustrated, the Grimmer brothers gave Mercury a deadline in October last year to meet them and explain his confession. When he didn’t, Australian MP Jeremy Buckingham used parliamentary privilege to name him and read aloud his confession.

Stephen Grimmer, Ricki Nash and Paul Grimmer have called on the suspect to ‘do the right thing’ and explain the confession he wrote in 1971

Now the DPP is prepared to review the decision to drop the charges if any new evidence or witness information emerges. Meanwhile a parliamentary inquiry in Australia will begin in May.

Directly addressing the alleged perpetrator, Buckingham said: ‘You are a coward, a slug and a murderer and you should do the right thing now, explain that confession you made in 1971 and admit to your egregious crime.’

Paul Grimmer, whose wife had to stop him lunging at Mercury when the charges were dropped in 2019, will not let up. ‘I want to be able to sit at my mother and father’s grave and tell them we finally got him.’

The family, including their cousin Dr Michael Grimmer in England, have worked on the case tirelessly and have given police 11 lines of inquiry.

Ricki says over the years the police have made ‘monumental mistakes’ – and he wonders if someone is protecting Mercury.

Ultimately, the damaged seven-year-old boy inside him needs a resolution. ‘I think I’ll still be scratching at the lid of my coffin as they’re putting me in the ground, saying ‘have you checked this?’ or ‘have you done that?’

‘We can’t live with ourselves without doing everything we can.’