Three years in to Graham Dwyer's relationship with Emer McShea he revealed an unusual, somewhat dark, sexual fantasy.

The trainee architect confided that he fantasised about stabbing a woman while having sex with her. He started to bring a kitchen knife into their bedroom, placing it on the floor as they made love.

Expand Close Emer McShea had a son with Graham Dwyer during their four-year relationship, whom she described as 'adversarial' Court Collins. / Facebook

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Whatsapp Emer McShea had a son with Graham Dwyer during their four-year relationship, whom she described as 'adversarial'

By the time their relationship ended a year later, he was holding the knife in his left hand during sex.

It has since emerged that Dwyer was the subject of a garda probe for making threats and harassing his former partner and mother of their son Sennan.

It is understood that Dwyer made what is called "sinister contact" with Ms McShea in 2009 and sources say that the former couple had "not seen eye to eye" for many years.

"There was an investigation but there was not enough evidence to bring it any further," a senior source said.

The Donegal woman apparently gave a lengthy, detailed statement to detectives about their relationship after his arrest for murder on October 17, 2013.

"I'd say she enjoyed reading that and she's delighted I'm in trouble," Dwyer told detectives, adding that their relationship - over in 1996 - had been "quite adversarial".

When she testified against her ex in the Central Criminal Court she spoke confidently, telling the court she identified him in CCTV stills taken from Belarmine Plaza, Elaine O'Hara's apartment block in Stepaside.

It's not known exactly when Dwyer's lust for knife play and blood-letting resurfaced - if it ever wavered.

However, it was not a feature of his marriage to fellow architecture student Gemma Healy, who he wed in September 2002.

Intelligent and attractive, the professional busy mother of his two young children appeared to be the ideal wife who worked hard, ran the home and enjoyed pastimes like sailing while her husband flew model aeroplanes and drove expensive cars.

At one stage she suspected that her husband was having an affair, but it appears he had managed to keep his desire for knife play and blood lust from her.

Gemma's world came crashing down one autumn morning, when detectives arrested her husband on suspicion of murdering Ms O'Hara. Teams of officers searched every corner of their family home in leafy Foxrock, including her children's bedrooms.

Throughout his detention, he told detectives he wanted to protect his wife and "preserve" his marriage. It was only then the other women in her husband's secret life were revealed.

The 'master' had two 'subs', who he had recorded graphic sex tapes with, women who he knifed and ejaculated on during sex.

An Englishwoman also appeared in some of the disturbing clips played in court.

Dwyer himself admitted in one fantasy he penned that he acquired "two fine subs over the years and having role play with others" after bondage, rape and stabbing became his hobby.

One was a professional woman living in Dublin, well regarded in her field of work.

The other was Elaine, a childcare assistant who had suffered severe mental issues since childhood. Desperate for love and a child - one Dwyer had promised to give her if she helped him take a life - she remained tormented by her inner demons.

She had even asked him to collar her - the BDSM equivalent of marriage.

Ms O'Hara's desire to be chained, even tied up overnight, brought her deep into middle Ireland's seedy world of underground sex and various niche websites, including alt.com, where she met Dwyer in late 2007.

Dwyer wiped tears from his eyes as his garda interviews about his home life were read out in court by prosecutors. It was the one and only time the unflappable and confident murder suspect showed any emotion during his 10-week trial.

"I'm a very lucky man, I want to keep it... and I want to keep Gemma," he had said during his 24-hour detention. "I'd like to preserve my marriage, thank you very much."

Irish Independent