David Beattie is a man who will be forever haunted by 'what ifs'.

The 61-year-old, who today lives on the sun-drenched plains of Western Australia, might appear to have it all.

He has a beautiful wife, Suzanne, and four grown-up children, three boys and a girl. He runs a successful building services company and lives in a modern three-bedroom house just a five-minute drive from the sparkling ocean.

But David harbours a dark and painful secret from his past – the very reason, in fact, which forced him to leave the UK and move to the other side of the world in a bid to escape the agonising reality of what happened in his youth.

Almost four decades ago, his fiancée, 21-year-old florist Diane Sindall, the love of David's life and his childhood sweetheart, was brutally murdered in Birkenhead, Merseyside, the town where the young couple had grown up.

She was found, half-naked and bludgeoned to death, with vicious bite marks and lacerations all over her body, in an alley in the centre of town, on the morning of Saturday, August 2, 1986.

The heinous crime sent shockwaves through the community – and indeed the nation – but no one felt Diane's loss more than David. The couple – the very picture of young, carefree romance – had been due to get married the following year, and were excitedly planning the small ceremony with their family and friends.

They had recently adopted a dog, a labrador called Whitbread, together, and planned to have children within the year.

But in an instant, the bright future they had dreamed of was cruelly erased.

David, then working as a car repairer, initially fell under suspicion for Diane's murder, and found himself interrogated by Merseyside Police for seven gruelling hours before being released. It was, he later said, 'a nightmare'. He was crying so much he could barely answer their questions.

In a heartbreaking tribute to his fiancée, published in the Liverpool Echo, David wrote: 'I am going to keep on loving you, because it's the only thing I want to do. I don't want to sleep. I just want to keep on loving you.'

At her funeral in October 1986, at the church where they were due to marry, he clung tightly to her mother, Wendy's, hand. In photographs from the day, grief is etched across his pale face.

As the police opened an investigation into what happened that awful night, when Diane, a part-time barmaid, ran out of petrol on a busy thoroughfare and walked into the dark in search of fuel, David couldn't help but dwell on tortuous thoughts of 'what if'.

What if Diane hadn't taken that job at The Wellington pub in nearby Bebington to earn extra money for their wedding?

What if he, who had kissed her goodbye as she sat on the sideboard at the Wallasey flat they shared before her shift that night, hadn't let her walk out the door?

What if he hadn't been out himself that night, celebrating the first anniversary of his car repair business with friends, and had noticed she was missing earlier, rather than when he got in at 2.30am?

What, he must have wondered, if there had been just a cupful more petrol in her blue Fiat van?

Speaking exclusively to the Mail this week, a family friend of David Beattie, who lives on the Wirral, said he had 'worked very hard to rebuild his life' after losing Diane.

He stayed in Birkenhead, where he mourned his fiancée and remained close to her family for 13 years before meeting someone else and eventually moving away.

He is, the family friend adds, now living a 'very happy life' in Australia. 'It hasn't always been easy but he never forgot the horror of Diane's killing,' they said. 'It's still with him and even though he's got on with things, it's something that you can never completely overcome.'

Another family friend recalled Diane's 'infectious laugh', and her closeness with David's family, particularly his sisters, who saw her as one of their own. 'David adored Diane and our parents doted on her,' they added.

'None of the family has ever got over her murder.'

But this week, of course, the heinous crime that rocked this community is back in the headlines, as Peter Sullivan, the man once dubbed 'The Beast of Birkenhead' and sentenced to life in prison for Diane's murder, was exonerated by the Court of Appeal after 38 years behind bars, the longest miscarriage of justice involving a living prisoner in British history.

The news will, David's family friend says, no doubt bring back 'a lot of painful memories' for him.

And there is another family for whom old memories are being dredged up: the Sullivans.

In the 14,113 days Peter Sullivan, now 68, spent locked behind bars, his loved ones never doubted him. The Peter they knew was not 'The Beast of Birkenhead', nor 'The Wolfman', as enraged headlines had branded him. 

Such monikers, his siblings told the Mail this week, have caused untold pain to Peter.

For the Peter they knew was harmless; a naive, socially-awkward young man, who wouldn't have laid a finger on anyone.

Growing up with his parents, younger sister and two brothers in a small terraced house in Birkenhead, he did not have an easy life.

Small for his age and lacking in intellect, he struggled at school, where he was tormented

by bullies. Pupils at Rock Ferry High on the Wirral used to call him names and beat him up. Once, a group forced him to eat metal nuts and bolts in the playground.

On another occasion, an older teenager threatened to set his two dogs on him unless he handed over his pocket money.

Unable to stand up for himself, Peter reluctantly obliged.

Speaking in 1987, the year his 30-year-old son was found guilty of Diane's murder, his father Charles Sullivan called him 'a complete coward'.

His mother Margaret insisted her 'placid' first-born was 'incapable' of carrying out such a heinous sexual attack. 'My son is no monstrous killer,' she said.

During police interviews, it was reported, he broke down in tears, crying out for his mother, to whom he was 'closer to… than anyone else in the world'.

All this has now been discredited, leaving Peter in the clear.

Shortly after 2pm on Tuesday, as his lawyers and siblings gave emotional statements outside court, he gathered his things – and, in a blacked-out prison van, was driven to freedom.

For the Sullivan family, it marks a new beginning. But it is also the beginning of something else, something more ominous: the search for Diane's real killer.

On Thursday, it was claimed that residents of local estates knew the real identity of the 'Beast of Birkenhead' but no one from the 'tribal' and 'tight-knit' communities were willing to name the killer 'for fear of repercussions', said RASA Merseyside, a charity set up in Diane's memory to provide support for victims of rape and sexual abuse.

The news represents an agonising blow for Diane's family – her father, Brian, brother Colin, and sisters Carol and Pamela – who do not want to comment on Peter's release.

Speaking after the trial in 1987, Diane's late mother Wendy said she still spent hours every day crying and thinking of her beautiful, vivacious daughter. She would continue to do so until her own death in 2003.

Many others in Birkenhead remember Diane, too, and the fear that gripped the town in the weeks and months that followed her murder. A memorial stone, erected in 1988 at the spot where she was killed, on a grass verge opposite the Pyramids Shopping Centre, was laid with bouquets of bright spring flowers this week.

Ann John, 75, is the former landlady of The Wellington pub, where Diane worked part-time behind the bar – and was one of the last people to see her alive.

She told the Mail this week she fears the real killer 'could be dead and buried by now'.

'It is all very sad,' she said. 'He [Peter] has lost 38 years of his life and you can't make that back up.'

Ann has fond memories of the shy, bubbly blonde who blushed at the attention of the pub's male customers.

'Diane was a lovely girl,' she recalled. 'She didn't mix with the punters. They were all touchy-feely and she would be highly embarrassed. Many of the lads offered her a date but she would say she was with someone and she wasn't interested.'

In the summer of 1986, Diane had taken a job at 'The Welly', as it was known locally, two nights a week to make some extra cash.

Having finished work at the floristry counter, inside her uncle's greengrocer in nearby Seacombe, on Friday, August 1, she popped home to the flat in Wallasey she and David shared, before heading to the pub for work at 8pm.

When Diane's shift ended around 11.30pm, Ann walked her to her van at the back of the pub and told her to go straight home.

'All I want to do is go home,' he wailed. 'I want my mum. Can't you let me go home? I can't take no more.'

This Peter, the one who sobbed in the Court of Appeal this week as he appeared by videolink from HMP Wakefield, is the one his family know and love.

His siblings have stood by him, as did his parents until their deaths in 1995 and 2013. So, the Mail has learned, did Peter's girlfriend, Mary Walker, who gave birth to their only child, a son, in January 1987, while his father was awaiting trial.

So sure was she of his innocence that she agreed to marry Peter while he was behind bars in March that year.

Speaking to the Mail, David Sullivan, Peter's youngest brother, told of the 'unreal' emotion felt in court on Tuesday when his conviction was quashed due to new DNA evidence that ruled him out of the attack.

'Peter fell apart; he was in bits,' said David, 63, who still lives in Birkenhead. 'He always knew he had not done it and now it has been proven.

'The whole case has been wrong – for both sides. It was wrong for us and it was wrong for poor Diane and her family.'

The momentous ruling came after a referral by the Criminal Cases Review Commission (CCRC) last year. Peter first lodged an appeal against his conviction 15 years ago, only to face rejection after rejection.

This week the court ruled that DNA retrieved from a semen sample found on Diane Sindall's abdomen contained a profile that did not match Peter's – and instead pointed to an unknown killer.

In 1987, the technology to test for such DNA did not exist, and Peter's conviction was based on circumstantial evidence, a series of jumbled 'confessions', unreliable witness statements, and bite mark evidence found on Diane's body that apparently matched his dental impressions.

'I remember that night she was starving,' she recalls.

'She was always hungry. She said she was going for fish and chips, and I said, 'I'll do you a sandwich'. 'She said, 'No, no, I want some fish and chips and I need petrol as well'. I told her to go and get the petrol first.'

Shortly after leaving, Diane ran out of fuel on Borough Road in central Birkenhead and began walking – presumably in search of a garage or bus stop.

She was spotted four times by passers-by before 12.20am; in one sighting, a taxi driver reported seeing her arguing with a man, whom he said she appeared to know.

Quite what happened next, and how Diane met with such horror, is not known.

Chillingly, witnesses reported hearing screams between 12.30am and 2am – suggesting a prolonged, barbaric attack.

Her half-naked body, with a fractured skull, facial cuts, mutilated breasts and lacerated genitals, was found by a dog walker the next morning.

A nationwide manhunt, involving 100 officers and over 3,000 witness statements, began. Weeks passed with no progress.

The women of Birkenhead were left in fear of going out alone, especially at night.

Two barmaids at The Wellington quit their jobs; one moved out of her flat because it was close to the murder spot.

But then, in September 1986, after a BBC Crimewatch reconstruction, police alighted on Peter Sullivan.

A witness claimed to have seen him near a fire on an isolated hill, in which some of Diane's belongings that were missing from her body, including her handbag, had been burned the day after the murder. 

Peter, something of a 'village idiot', didn't initially seem to fit the bill.

As a teenager, he had developed a taste for petty theft, and earned a reputation as a liar, a Walter Mitty-type who told tall tales.

His own parents regularly reported him to the police for stealing money and electrical goods from the family home.

He had 18 previous convictions – for theft and stealing cars – but had never been linked with more violent or sexual crimes.

Now, with a heavily-pregnant girlfriend at home, he seemed to be on the straight and narrow.

When quizzed about the night Diane died, however, the unemployed labourer gave several 'completely different' accounts of his movements.

He had, it was alleged, been drunk after a darts match at a local pub when he staggered out on to the street.

The next day, Peter allegedly 'confessed' to the murder, only to retract his confession, and later reinstate it.

Two days passed before he was given access to a solicitor, after which he retracted his confession again and told police he had made it up.

Fourteen months later, on November 4, 1987, a jury found him guilty.

At home in their council maisonette, Mary – a divorcee who had been with Peter for 12 years, since he was 18 and she 24 – was devastated. Their son was just ten months old, while Mary's older children – three sons with her first husband, Bernard Linford – were teenagers.

Linda Linford, 63, who married Bernard after he and Mary got divorced, knew the family well and recalls Mary's visits to Peter in prison.

'When Peter was put away, one of Mary and Bernard's sons would look after their baby while Mary was visiting him in prison on the Isle of Wight,' she told the Mail this week.

'Bernard told me that Mary never believed Peter was guilty.

'But she got a lot of grief from local people in Liverpool after the marriage. They thought she shouldn't have married him.

'So, I think for her own safety, she had to pretend she wasn't with him anymore.'

Peter, Linda says, was a 'sound bloke' whose arrest came as a 'real shock'.

'What really annoys me is that the real murderer could be dead now and [he] would have got away with it. It's shocking and awful and I hope Peter gets some compensation.'

Certainly, Peter could be in line for a £1million payout from the Ministry of Justice – the maximum amount available to those wrongfully convicted.

And there may be other wrongs to be righted, too.

Questions have been raised over the handling of the case by Merseyside Police, particularly Peter's lack of access to legal representation, the focus on now-discredited 'forensic

dentistry' that apparently matched his dental impressions to bite marks found on Diane's body and statements from unreliable witnesses.

Officials involved in the case have also been named and shamed, among them former CID chief Tom Baxter, who spearheaded the investigation, and was also involved in clearing the detectives who wrongfully set up four men for the murder of paperboy Carl Bridgewater in 1978.

But Merseyside Police point out that Mr Sullivan's quashed conviction made no criticism of police. Since 2023, a new investigation into Diane's murder has been in motion, with DNA screening conducted as far afield as Swansea, Perth, London, Hull and Newcastle, to try to find her killer.

What any of this means for Peter Sullivan won't be clear for some time. For now, he is lying low, enjoying his newfound freedom with his family.

Speaking outside court this week, Peter's sister Kim Smith, 65, said: 'We've got Peter back, and now we've got to try and build a life around him again.' The same cannot be said for the bereft family of Diane Sindall – or indeed David Beattie.

'When Peter Sullivan was jailed we thought at least Diane's killer is off the streets,' said David's family friend.

'Now we want to know why it's taken so long for them to realise they'd got the wrong man. I can't begin to imagine how hard this is for her family. They deserve justice after all this time.'

• Additional reporting: Andy Russell and Jan Disley