It remains one of the most high-profile crimes in the history of the State, but a new documentary recalls how the killing of Elaine O’Hara was nearly a case of the perfect murder.

For 14 months after he had killed the Dubliner, Graham Dwyer must have believed he had got away with murder.

But in the unseasonably dry August of 2013, water levels had fallen to an almost unprecedented low at a reservoir in Roundwood, Co. Wicklow.

And with them, the best-laid plans of the respected Dublin architect, who was also a seemingly happily-married father-of-three, began to unravel.

A year after child minder Ms O’Hara had gone missing in August 2012, some men spotted items in the muddy water bed which was usually covered by water – they turned out to be sex toys and some items of clothing. They took them to the nearest police station.

A few days later a diligent local garda decided to go back for another look. He climbed down the bank and there, glistening in the mud, was the unmistakable gleam of a pair of keys.

Stretching down, he retrieved them and brought them back to his station from where they were sent for analysis. Eventually the supermarket loyalty fobs on the keys would identify them as Ms O’Hara’s.

It remains one of the most high-profile crimes in the history of the State, but a new documentary recalls how the killing of Elaine O’Hara was nearly a case of the perfect murder

It was a key piece in the jigsaw, which would culminate in October 14, 2013, with gardaí knocking on Dywer’s door and arresting him.

But they had yet to understand the extent of the horror that had unfolded, and many who were witness to its details, have never been able to forget it.

Some of those investigating gardaí have now contributed to a new episode of RTÉ’s The Case I Can’t Forget.

In September 2013, a month after the keys were discovered but not identified, a dog walker on Killakee Mountain in Wicklow had discovered human remains scattered through the woodland. 

The remains were quickly identified as those of 36-year-old Ms O’Hara, who had disappeared in August 2012.

Because of her long struggle with mental health difficulties, her family feared she had taken her own life at sea.

Her car was found at Shanganagh cemetery in south Dublin, the graveyard where her beloved mother was buried and which she had visited with her father on the day she disappeared.

With almost no forensic evidence and an undetermined cause of death, the investigation pivoted entirely to Ms O’Hara’s digital footprint.

Detective Sergeant Grace O’Boyle coordinated an immense volume of material — CCTV, phone data, witness statements and online activity — to shape a coherent timeline that might explain how her body had ended up on Killakee Mountain.

‘Having a crime scene in a forest, in a wooded area, it’s not conducive to a criminal investigation,’ she tells the programme.

‘You’re not going to have CCTV cameras. You’re rarely going to have witnesses. So on the ground you’re working around and in, it just creates its own problems.

‘Crucially you’re out in the elements. You have animal interference and then to distinguish between what is animal behaviour and any potential evidence.

‘Sixty five per cent of the skeletal remains were recovered. It was a female, roughly between 35 and 40. Elaine appeared to have died where the body was discovered.’

The discovery of the corpse and the identification of the keys and phones nearly an hour away in Vartry Reservoir eventually led gardaí to conclude that, not only was she in a manipulative BDSM relationship with her killer, but also that she had met him on the day she disappeared.

Smirking killer Graham Dwyer after his conviction 

As Detective Sergeant Kevin Duggan reconstructed Elaine’s final movements through detailed CCTV analysis and senior crime analyst Sarah Skedd examined phone records and text messages, one name emerged from the reams of data – Graham Dwyer.

From the outset Detective Duggan knew this case was different: ‘I said to myself this is going to be the most significant investigation that you will ever be involved in.’

A further breakthrough came when the two phones taken from the reservoir bed were able to be reconstructed. 

They were both able to be switched on and all the text messages were readily available and investigating gardaí had the notorious ‘master’ and ‘slave” phones as they came to be known during the ensuing trial.

Detective Duggan described the discovery of the two mobile phones as ‘a miracle’.

Ms Skedd set to work on finding who owned the master phone: 

‘I started looking for unique journeys and I found there was a day when the ‘master; phone was used in the east of Galway city in the morning and had returned to using cells in the southeast of Dublin city early in the afternoon.

‘So the only realistic way of making the journey in that timeframe is to travel along the motorway network passing through the M6 Toll near Ballinasloe and then through the M4 toll near Enfield.

‘[Through CCTV] we found a vehicle that met those criteria that was registered with an owner at an address in south county Dublin.’

To this day, colleagues and former friends say they cannot believe they were duped by Dwyer.

‘He was the most vanilla person you could ever meet, he was so normal, even dull,’ one recalled.

The investigating team were hugely trepidatious coming up to the trial. For them, they hadn’t got Dwyer until the jury foreperson read out a guilty verdict.

‘I felt enormous pressure and anxiety coming up to this trial,’ Ms Sked recalled.

‘It was very important to me that the work that I had done with the investigation team, that it was, most importantly, a true and accurate reflection of what had happened.’

After an eight week trial in 2015, the jury found Dwyer guilty in a unanimous decision.

The year after he was caged, the arrogant killer boasted to a young female pen pal that he would be freed on appeal. 

He suggested that statements made by State Pathologist Marie Cassidy would help to secure his appeal.

The depraved south Dublin architect made the claims in a series of letters, in which he oozed confidence and repeatedly maintained his innocence, while admitting to ‘extreme sex’.

American psychotherapist Dr Robi Ludwig said Dwyer was ‘flirty’ and ‘definintely had an agenda’

He wrote to the student at the time: ‘I will buy Dr Cassidy a pint and take you out to celebrate!! He he.’

He was referring to comments by the pathologist that she had believed a not-guilty verdict would be returned in his case due to a lack of physical evidence.

However, the Supreme Court would eventually reject his appeal when the judges ruled unanimously that evidence from mobile-phone data at his trial had been admissible.

Asked to analyse Dwyer’s letters to his young pen pal, American psychotherapist Dr Robi Ludwig previously told MoS: ‘He definitely has an agenda, his mindset is he is not guilty.

‘I don’t see any signs of depression. He’s focused on his goal, he’s on a mission, he’s feeling positive.’ 

She added that if you are wrongfully convicted ‘it’s not a happy place’. She said: ‘He’s taking action, he’s on a mission, he’s working with people, he’s flirting and you’re not depressed if you’re flirting. 

‘I think he loves the attention, and at another level, if you are into sadomasochism, for him this is the masochistic part, getting punished and waiting to get out.’