The relationship between Graham Dwyer and Elaine O'Hara was unlike any relationship ever seen in an Irish court, and it revealed more about the two than either had ever told their loved ones.

On August 20th, 2012, two days before she disappeared, O’Hara awoke in her room at St Edmundsbury psychiatric hospital in Lucan, in west Co Dublin. The 36-year-old was greeted with a text from Dwyer. “Morning slave, looking forward to seeing you Wednesday.”

It was not the first time he had called her that. Their master-slave relationship dated back to 2007, when they met on alt.com, a website for people with interests in bondage, domination, submission and masochism. O’Hara used the website because of her personal interests and to help her cope with her social awkwardness. Since the age of 12 she had had fantasies about being tied up and punished. The fantasies, coupled with a borderline personality disorder that manifested as cripplingly low self-esteem and depression, had first led her to the hospital in 1992. She was admitted after an incidence of self-harm. She had a propensity to cut herself. She had overdosed twice. Her psychiatrist, the late Prof Anthony Clare, perceived that she had wishes to be a boy; she did not dress in a feminine way.

By August 20th she had been in hospital 14 times; her most recent admission had begun on July 14th, when she rang the hospital to tell them that she had made a noose to hang herself.

Dwyer was drawn to alt.com because of his need to find a woman who was interested in submitting to his desire to spill blood. The 42-year-old was not really interested in being a “master”. He tried to meet O’Hara’s desire to be tied up regularly, to have someone to make decisions for her and to tell her what to do in every aspect of her life. He occasionally succeeded, but more often O’Hara was frustrated with him and disappointed by the lack of attention he gave her. She told him that he wanted her only so that he could meet his own needs.

It was unsurprising that Dwyer could not spare the time to “play” with O’Hara; the Cork-born architect lived with his wife and two young children in Foxrock, in south Dublin. He also had an adult son by another relationship. Dwyer had a successful career at the firm of A&D Wejchert & Partners. He also had a time-consuming hobby: model aircraft took up a lot of his spare time and energy. It also meant that his family was used to him not being around on Wednesdays after work, when he set aside time to indulge in flying.

From her hospital room on August 20th O’Hara addressed Dwyer as sir. He told her, “You must be punished for trying to kill yourself without me.”

Dwyer liked to remind O’Hara of a promise she had made him in the early days of their relationship: if she wanted to die, she would let him kill her. It was a recurring theme; he often tested her to see how close to suicide she was, and the conversations often ended with her asking him to stop. She had asked him to kill her once, while in the depths of despair. He had not been prepared at the time, but in August 2012 he was ready.

O’Hara’s latest stay at St Edmundsbury had come after the longest break she’d had from hospital; she had not been admitted since early 2009. The medics linked her distress to the loss of Clare, her long-time psychiatrist. They were unaware that the admittance followed only a few months after Dwyer videoed himself stabbing O’Hara during sex. The relationship broke up not long after that, and O’Hara seemed to gain in strength once again.

Despite her mental-health difficulties, and physical conditions that included diabetes and asthma, she worked two jobs: as a shop assistant at Robertson newsagent’s in Blackrock and as a childcare assistant at St John’s school in Ballybrack. She was also studying childcare.

Her relationship with Dwyer was reignited in March 2011. He contacted her from a new 083 mobile phone he had bought. He had given a false name when he bought it, Goroon Caisholm, and given an address similar to his sister’s in Tipperary. Even at this early stage, it appeared, Dwyer was watching his tracks.

O’Hara spent the rest of August 20th in hospital, preparing for her return home. She told medics that she was nervous but excited, looking forward to volunteering at the Tall Ships festival that Thursday. She chain-smoked with other patients and talked incessantly about the event. She would be picked up early on Thursday morning by her father’s partner, Sheila Hawkins, who would drive into the city.

Dwyer spent his day as normal, at work and at home, with no sign that he was planning anything. He had by now mastered the art of the double life; skilled with computers, he had set up separate profiles for himself and his wife on their home PC, so she could never log on and accidently find the images he liked to view and the documents he had written. They included a graphic and sickeningly violent fantasy about murdering a young woman he was in contact with online, Darci Day.

When she awoke on August 21st more texts were waiting for O’Hara. She and Dwyer were using prepaid phones that he had bought in November 2011, assuming them to be untraceable.

Dwyer told her: “If it doesn’t work out this time the way out is through me.” O’Hara said he didn’t understand suicide, that it can happen quickly. He responded that it had to be him doing it and that he was ready for it. “All you have to do is tell me you want out and then get in to bed and wait, max 12 hours.” She told him to forget about it.

Although she had been pandering to him, she now accused him of being selfish. Then, apologising, she resumed her submission, and said she wanted to be a good person, slave and friend. She said she supposed she had a punishment coming up. “It’s up to me and you have a big punishment coming up, knife in the guts,” Dwyer told her.

He had had fantasies about stabbing a woman to death during sex since he was a teenager. He confided his fantasy to Emer McShea, with whom he had a son, Sennan, in 1992. The two met in their teens. The relationship lasted until they were in their 20s, when McShea moved back to her home in Ballyshannon, Co Donegal. After Dwyer told her about his fantasies he began bringing a knife into their bedroom, first leaving it on the floor, then graduating to holding it in his hand during sex. He never got as far as cutting her, but, it seems, the sadist in him had been released.

By 2005 he had met women through alt.com, women who were more amenable to his sexual desires, women who would let him use a knife on them. Later, when he met O’Hara, the need to cut became more intense. He told her in one text, “my urge to rape, stab, kill is huge. You have to help me control or satisfy it.”

On August 21st Dwyer told O’Hara she would be “well bound and gagged, tied to a tree deep in the forest.” “I have a spot picked out,” he said.

He had threatened to kill her in the past. It became a theme in their relationship after they reconciled in 2011. He would tell her to find a woman for him to kill; otherwise he would have to stab her. At the outset he coaxed her back into the relationship by promising not to stab. But, inevitably, he managed to reintroduce the knife to their sex life. At first it was to be only one cut, then only for punishment, but soon the wounds were multiple. There were times O’Hara wrested back control from him, telling him that she could not give him what he needed. But he always got what he wanted, to the very end of their relationship.

O’Hara tried to be assertive on August 21st. She said she was not leaving her apartment. She had bought the apartment, in Belarmine Plaza, in late 2010, as part of an affordable-housing scheme. It was not her first independent home. When she moved away from her family in Killiney in 2005, she initially lived in a converted garage at Rockville Crescent in Blackrock. From there, in 2008, she moved to a bedsit, in Ardmeen Lodge, nearby on Newtownpark Avenue; then she bought Belarmine Plaza.

O’Hara told Dwyer he would have to drag her from her apartment. He responded that she would do what she was told and that he wanted outdoor play. “I found a really, really remote place no one will find us,” he said. She asked if she had to be naked. He said she did. “I don’t want blood all over your clothes,” he said.

She said she was frightened.

“Trust me, it will be exciting.”

O’Hara asked if she’d have to drive. A bit, he said.

“Now I’m really scared,” she replied. He told her not to be, to look forward to being reunited with her master.

By 5pm on August 21st Dwyer had taken delivery of a hunting knife. He had ordered it online, to be sent to his office, marked private and confidential.

He said, “I’m heading out to the spot now to double check.” He was coming from work when he sent that text, and he didn’t drive straight home; instead he drove up to Killakee Mountain.

That evening medics regarded O’Hara as cheerful and positive, but one nurse had concerns. Rosetta Callan is in O’Hara’s room around 11pm to see that she settled down for the night. O’Hara confided that she is worried about a man who had a key to her apartment and bothered her. She did not give away the details of their relationship. She had always been careful about who she talked to.

She told her father only once that she was in a relationship with a man who tied her up; later she said it was over. She dropped hints to the women she worked with, revealing only partial information and once, accidentally, showing photographs of bondage gear on her phone.

She confided most in a friend who had been a patient in the hospital. She told Edna Lillis that a man was cutting her. She was warned to be careful.

Keeping her promise not to tell people who Graham Dwyer was, O’Hara did not give Callan his name. The nurse suggested she contact the Garda. O’Hara said she wouldn’t do that; the man had small children, and she would not like to see them hurt. It was the closest she ever came to telling someone about the great trouble she was in.

The next morning, on August 22nd, O’Hara was ready to go home but still nervous. At 8am she texted Dwyer, to say the hospital was a “pain in the ass” but at least she knew she was safe there.

“I’m just so scared . . . did you know sir, I’m scared of you, you have this hold over me that terrifies me,” she said.

She asked that he not mention killing for a while, until she had settled back to life. He said that was fine, “but tonight’s punishment will be like me pretending to do someone for real, ok?”

He said it was important to him that she feel it was real. “Every time I stab and strangle you I want you to think this is it. And every time I let you live you owe me your life and are grateful and worship me x.”

She agreed. “Now can we stop talking about it?”

It was shortly after 10am, and Dwyer was texting from work. He left his home at the usual time and arrived in the office at 8.30am. It was a normal day for him.

Shortly after noon O’Hara was released from hospital. She texted to let Dwyer know and asked for any instructions.

He told her to have a bath and to shave.

“No underwear, not even a bra. Loose clothes and footwear for bit of mud. Make sure you are fed, Take painkiller at 5pm.”

She worried about the pain afterwards and reminded him that she had things to do on Thursday, that she was committed to the Tall Ships festival.

“You will have stab wounds, you know the drill. Last few didn’t bleed but these will.”

“I want you to park at Shanganagh Cemetery at 5.30pm. Leave iphone at home, just bring slave phone and keys. You will get further instructions there,” he said.

O’Hara asked if they would still do it if it was raining. He said they would, and she complained that it would be cold.

Dwyer spent the afternoon at work. He could not have been too focused on what he was doing. He had his hunting knife and was mentally preparing to use it. He also had his killing bag, a rucksack containing other knives, and items such as duct tape. There may have been chloroform; he had tested the chemical on himself, to measure its effects. He had been keeping the killing bag at O’Hara’s apartment but took it from there on August 15th.

After dropping her bags home O’Hara went to visit her father, who was minding his granddaughter. She was very close to her father; he believed she saw him as her best friend. They took a drive to Woodie’s and then went on to Shanganagh Cemetery, where O’Hara’s mother was buried. She died in 2002, and her loss had a strong impact on her daughter, leading to a series of admittances to St Edmundsbury.

They had lunch, and O’Hara took her niece to the green across the road from her father’s home to play. She gave the child a bracelet she had made, before going back to her apartment at 4pm. She made a mundane visit to the pharmacist, filling the prescription given to her earlier at the hospital. She called the newsagent’s where she worked to ask about shifts.

Shortly before 4pm Dwyer texted her again. He told her it’s never as bad as she thinks it’s going to be. He added an emoticon, a smiley face.

At 4.23pm she responded “yes it is, sir”. He told her to enjoy being told what to do. She said that’s easier said than done.

“Just empty yourself and become nothing. You are properly a piece of slave meat. Your only job is to serve,” he said.

At 4.50pm O’Hara asked if she could bring socks and an inhaler and wondered when she’d be back. She also said she hadn’t had time to eat.

“You should be back at car about eight,” he said. “More painful getting stabbed on an empty stomach, suit yourself.” Dwyer was still at work, but he was preparing to leave.

At 5.05pm O’Hara left Belarmine Plaza for the last time. She had left her iPhone behind. She drove out in her Fiat Punto and waved at a neighbour. As she was driving she got a text from Dwyer, telling her to “stay on outer bit on way in”. His phone had used a cell tower at Montrose; he was en route to Shanganagh.

At 5.20pm O’Hara was approaching the cemetery. She texted that a lot of the children she worked with lived “around here”. Two minutes later she told Dwyer she had arrived.

Three minutes later Dwyer was passing Cornelscourt on the N11. He instructed her to take only her keys and her slave phone and to make her way to the park next door.

“Text from middle,” he said.

She asked if she could take her inhaler. He said she can.

At 17.39pm he told her to “cross the railway bridge into the next park near the cliffs”. By this time his phone was using masts at Fassaroe, in Co Wicklow.

O'Hara couldn't find the railway bridge. She stopped a jogger, Conor Guilfoyle, and asked for directions. She found the railway bridge.

“Cross bridge and head to opposite end of park near steps to sea,” Dwyer instructed. He was closer still; his phone was using a mast at the Leisureplex in Bray.

“Steps here,” O’Hara said.

Dwyer sent his last text from his master phone at 6pm, using a mast at Shankill.

“Go down to shore and wait.”

She did as she was told, and there were no further texts from either phone. Dwyer switched his work phone off at 6pm and did not turn it back on until 9.15pm.

He drove to Quinn’s Road, close to the shore, where O’Hara was waiting. She joined him in the car, and they travelled together to Killakee Mountain, to the place he had chosen for her end. She had little with her except the clothes on her back, her slave phone, her inhaler and her keys.

He had what he needed; perhaps he left it there on his visit the night before: the killing bag, the knives, the sexual paraphernalia of cuffs and gags and mask. Or perhaps he took it from the boot of his car, before leading her deep into the forest. Once there he did what he had been promising to do since at least 2011.

Afterwards he walked back to his car and filled it with the belongings he would dump in the Vartry reservoir. He left her on the mountain.