Prosecuting lawyers have described the relationship between Elaine O'Hara and Graham Dwyer as entirely predatory.
Mr Dwyer, 42, of Kerrymount Close in Foxrock, denies the murder of 36-year-old Elaine O'Hara at Kilakee Mountain in Rathfarnham on 22 August 2012.
Prosecution counsel Sean Guerin said in his closing speech to the jury that the prosecution case was that Mr Dwyer murdered Ms O'Hara by stabbing her for his sexual gratification.
He said the prosecution case was that he arranged to lure or bring her up the mountain at Kilakee on the evening of 22 August 2012 for the purpose of satisfying a deep-seated sexual desire.
He said Ms O'Hara had the misfortune to be in circumstances where she was amenable to being used in that plan because she was in an abusive and manipulative relationship with Mr Dwyer.
The prosecution claims this enabled him to isolate her and exploit her for the sexual purpose he had in mind, in a way that would lead more or less everyone to think she had died by suicide.
Mr Guerin said this plan very nearly worked out for Mr Dwyer.
'Wickedness hiding behind the mask of pity'
Mr Guerin said a common theme of the relationship between Mr Dwyer and Ms O'Hara was "wickedness hiding behind the mask of pity".
Mr Guerin said Ms O'Hara was a very sad person, troubled by thoughts of her own self worth and did not value herself.
Hospital records described her as having a supportive dad but no friends.
Mr Guerin said that was the tragic, sad and unfortunate situation which Mr Dwyer was only too happy to take advantage of.
Mr Guerin said it appeared the relationship between Mr Dwyer and Ms O'Hara which ended on the side of Kilakee Mountain in August 2012, appeared to have begun via a website in late 2007.
He said there was an old Irish saying translated as fighting is better than loneliness. He said being lonely was worse than an awful lot else and people settled for situations in which they were unhappy with rather than being alone.
He said what Mr Dwyer would do with Ms O'Hara was deeply damaging to her.
Mr Dwyer was offering a troubled and sometimes suicidal woman "help" in the form of a way out.
Mr Guerin said the videos they had seen of Mr Dwyer with Ms O'Hara had shown a "vicious, brutal act of violence" perpetrated by Mr Dwyer on her in which he says to her at the end "that wasn't bad wasn't it".
He said that suggested Ms O'Hara had to be convinced or persuaded to take part and Mr Dwyer was able to overcome her unwillingness to be a victim of an attack.
He said Ms O'Hara's fear of loneliness leads her into the situations she finds herself in.
He said from a very early stage, Ms O'Hara made it very clear that she did not want to be stabbed. She had told him within 11 minutes of him first making contact with her in 2011 that she was not into blood any more.
He said Mr Dwyer had told a very different story in his interview with gardaí and had lied through his teeth about his relationship with Ms O'Hara.
In his fourth interview he had claimed "that weird stuff wasn't for him".
Mr Guerin said the tragedy of the combination of Ms O'Hara's weakness and her availability to Mr Dwyer meant that ultimately she was the easier target for him than others.
He said Mr Dwyer showed "pure wickedness with a mask of pity".
When she was unwell he offered to stab her. He said this person, posing as someone who cared about her was pushing her towards the edge.
Four strands to prosecution's case
Mr Guerin said there were four broad strands to the prosecution case.
The prosecution claimed that it could connect Mr Dwyer to the death and disappearance of Ms O'Hara.
Mr Guerin also said the prosecution case was that at the time of Ms O'Hara's disappearance and beforehand, Mr Dwyer had not only the desire or sexual fantasy but actually the intention of murdering Ms O'Hara by stabbing.
He said the firm and definite intention existed in Mr Dwyer's mind.
Mr Guerin also said the circumstances of Ms O'Hara's disappearance reflected almost point-by-point the detailed plan Mr Dwyer had elaborated over a period of time to fulfil that sexual desire.
Mr Guerin said the fourth issue the prosecution had to address was any other possibility that might exist as to how Ms O'Hara met her death.
He said two issues arose here - was there someone else involved or the possibility of death by suicide.
He reminded the jury that it was the responsibility of the prosecution to prove its case.
He said the defence did not have to prove anything.
Links between Dwyer and two mobile phones outlined
Mr Guerin took the jury through the first strand of the prosecution case and outlining the links the prosecution says exist between Mr Dwyer and two mobile phones alleged to have been used by him to contact Ms O'Hara.
Mr Guerin said the most striking feature of the links between the phones and Mr Dwyer was the content of the text messages sent.
He said when you look at the text messages you find that the messages hold up a mirror to the life of Mr Dwyer.
You see reflected in them exactly what he is doing and exactly what is happening in his life to an extent that is extraordinary and would be utterly impossible if anyone other than Mr Dwyer was using the phones, he said.
Mr Guerin also pointed to the top-ups bought for the 086 or "master" phone found in the Vartry reservoir which were bought near Mr Dwyer's office, in a shop near his home and near the offices of An Bord Pleanála on a day Mr Dwyer was attending a hearing there.
Mr Guerin also reminded the jury that an 083 phone was saved in Ms O'Hara's computer and in a diary as "Graham's phone number".
He went through some of the texts sent by the 083 phone and the links between them and Mr Dwyer's life according to the prosecution evidence.
Mr Guerin pointed out a number of links between the messages sent by two mobile phones and Mr Dwyer.
There were messages relating to the birth of a child - on the same day and with the same name as Mr Dwyer's daughter.
There were messages referring to the name of his other child, as well as to wearing "polo necks" like his.
There were references to the cost of repairs to his car, to buying a bike, to a pay cut and coming fifth in flying, as well as attending conferences, meeting the Polish ambassador and attending a "family thing".
Mr Guerin said all this content mirrored the details of Mr Dwyer's personal life.
Mr Guerin also said there was nothing in the usage of Mr Dwyer's work phone and the two phones the prosecution claims he was also using, inconsistent with the suggestion that it was the same person who used the phones.
He said the pattern of cells used by the phones was remarkably consistent.
He said the phones told the story of Mr Dwyer's life in this period - all the details relating to his work life, social life, family life were confirmed by the evidence the jury had heard.
He said there was no suggestion in the thousands of calls and texts that different people were using Mr Dwyer's work phone and the other phones.
Mr Guerin said wherever Mr Dwyer went the phones went too.
They were stuck to him like a shadow.
Mr Guerin said this was circumstantial evidence - evidence of circumstances which when taken together left open no other possible conclusion but that these were his phones.
He said it was up to the jury to be satisfied beyond reasonable doubt that this case had been made by the prosecution.
Mr Guerin said this case was about a person who has the most extraordinary and disgusting fantasies, who goes about making them real.
He asked what Mr Dwyer intended to do on 22 August 2012.
He said the prosecution case was that there was a very firm, clear and determined intention to do certain things. He said this was not merely a desire.
He said there had been a lot of talk about "fantasy". He said this could sometimes mean orcs and elves and unicorns and leprechauns.
But he said fantasy could also mean desire, particularly in a sexual context. He said fantasy was the expression of a desire.
It may not be real but it is something the person who has the fantasy wishes was real.
Mr Guerin said the evidence of Mr Dwyer's ex-girlfriend Emer McShea was not challenged in court.
He said to make his fantasy reality, Mr Dwyer had to find victims who would willingly submit to what he had in mind. Preferably willingly, but if not, any victim.
Mr Guerin said Mr Dwyer had repeatedly identified real people as victims of his fantasies, including Darci Day, Ms O'Hara and Rowena Quinn - an auctioneer who had the misfortune to work in an office across the road from Mr Dwyer's workplace.
Mr Guerin said documents found on a hard drive in Mr Dwyer's home imagined in vivid and very graphic detail the most vile and sickening torture and murder of women.
Mr Guerin said the jury was entitled to draw inferences about the relationship between Mr Dwyer and Ms O'Hara from the evidence.
Mr Guerin said from the very outset Mr Dwyer had a very limited practice in mind in his relationship with Ms O'Hara - that was to use her as a victim for the sexual fantasies he had.
He said the tragedy of the case was that the warning lights the texts very clearly caused to flash do not seem to have been sufficient to warn off Ms O'Hara.
Mr Guerin said Mr Dwyer saw nothing in Ms O'Hara's psychiatric difficulties, nothing but an opportunity to achieve what he wanted.
He said the relationship between Mr Dwyer and Ms O'Hara was entirely predatory.
Like any predator, he said Mr Dwyer had an eye for the weak.
He could see Ms O'Hara's loneliness, her isolation, her friendlessness and her weakness.
He saw an opportunity to separate her from the flock.
He saw an opportunity to get her on her own, to undermine her sense of self until she lent herself willingly to the plan he had in mind: the only thing he ever saw in her - to be a victim of stabbing.
He said in August 2012, all the pieces fall into place.
He said the fact Ms O'Hara was in hospital, made it all the more likely it could be suggested and believed that she was suicidal.
He said Ms O'Hara had said she did not want his child, did not want his money, did not want anything to do with him.
He said in July and August 2012, the opportunity arose to take advantage of her in the way he had intended.