Lawyers for a 50-year-old man accused of murdering his alleged love rival and putting his body in an underground tank on his former girlfriend's land have told the jury that there are deficiencies in the prosecution case that "love and money" were at the heart of the motive.

Patrick Quirke, of Breanshamore, Co Tipperary, has pleaded not guilty to murdering Bobby Ryan, a part-time DJ known as Mr Moonlight.

Mr Ryan went missing on 3 June 2011 after leaving his girlfriend Mary Lowry's home.

The prosecution claims Mr Quirke murdered Mr Ryan so he could rekindle an affair with Ms Lowry.

Defence Counsel Bernard Condon was continuing his speech to the six men and six women on the jury.

He told them they should not look at the quantity of the evidence in the case but its quality. He said that a lot of the inferences they were being asked to draw had nothing to do with murder.

Mr Condon said they should have concerns about the evidence given by Mary Lowry and the manner in which she was prepared to revise history. He said she was someone who was not capable of telling the truth.

He said Ms Lowry described her relationship with Mr Quirke as a "sordid affair" but he said this was revisionism and someone wanting to put themselves in the best light having made decisions they now regretted.

The suggestion, Mr Condon said, that Ms Lowry was a vulnerable person who was controlled by Mr Quirke was based almost entirely on the uncorroborated and unsupported evidence of Ms Lowry.

He alleged that Ms Lowry had presented her evidence in a manipulative manner and pointed to what he claimed were inconsistencies in what she had told gardaì about certain events and what she had said in court.

Mr Condon said she had told a number of "out and out lies" to the jury and asked the members if they could accept the testimony of such a witness beyond reasonable doubt. Much of what she said about Patrick Quirke, he said, was "divorced of corroboration".

Mr Condon said it was possible that Ms Lowry did not want to admit to herself that she had rekindled the relationship with Mr Quirke after Mr Ryan went missing in June 2011.  

He said that was "absolutely fine" and people had all sorts of coping mechanisms.  But he said the problem was a witness bringing that revisionist history, delivering it in the witness box as fact, and inviting the jury to draw inferences negative to another person, in a murder case.  

Mr Condon said all anyone wanted from Ms Lowry was the unvarnished truth, "not the opinion column".  

He said the jury were entitled to the unvarnished truth, "warts and all".  

If a person was choosing to present evidence in a way that supported their current view of themselves, then that was a very dangerous witness for the person against whom the allegations were being made.

Mr Condon said at its heart, the prosecution was saying to them that "love and money" was a motive to kill someone. He said there were deficiencies in the way evidence about this was being presented by Ms Lowry.

He urged them to be cautious about a "Dear Patricia" letter written by Mr Quirke and published in the Sunday Independent in 2011. He said Mr Quirke had accepted in this letter that the relationship was over.

Mr Condon said there was no evidence to suggest that Mr Quirke was in severe financial difficulty.

He urged them not to be misled by the suggestion by gardaì in their interviews with Mr Quirke that he was getting "sex on demand and money on demand" from Mary Lowry. That was a tabloid headline, Mr Condon claimed, and it was not true.

He said Mr Quirke and Ms Lowry were a grown couple who had a consensual sexual relationship which they both regretted. "We can regret our decisions," he said, but can't come in and rewrite history.

It was a relationship which benefited both of them, he said, although in hindsight, Ms Lowry may regret it. He urged the jury to read the interviews with Mr Quirke with open minds, not with the "jaundiced spin" the prosecution would have put on them.

Mr Condon said the prosecution was asking them to draw inferences which to a large extent did not go very far and did not prove murder. He said behind the prosecution case was a "crumbling edifice of almost nothing".

Mr Condon said Mary Lowry had told "an obvious lie" to the jury when she told them she hadn't known Patrick Quirke was going away with his family on the morning Bobby Ryan went missing.

He said she had given evidence that she had seen Mr Quirke at around 8.30am on the morning of 3 June 2011, and that he was "hot, sweaty and bothered looking".

He claimed she had suggested there was something odd about Mr Quirke being around at that time, in order to poison the jury. And she said she didn't know he was going away. 

But Mr Condon said on 9 June 2011 Ms Lowry had told gardaí Mr Quirke was going away with his family  and was probably trying to get some jobs done.

Mr Condon asked what was going on. 

He said this was a piece of the "most devious poison" delivered "across the face" of the Central Criminal Court in many a year.

He said this evidence was an attempt to put into the jurors' minds that Mr Quirke was up to no good.

He said she had not told the gardaí about seeing Mr Quirke look hot sweaty and bothered until after the body of Mr Ryan was found. 

And he said she knew had been going away for the weekend.  So what was she trying to do in the witness box, he asked, and why was she trying to do it.

Mr Condon again said the case was a forensically barren landscape and the jury was being asked to make very important decisions on evidence that was not reliable and strong. 

The prosecution alleged Mr Ryan had been badly beaten with an implement but no implement had been shown to the court.

He said it was alleged that Bobby Ryan had been killed some time after 6.30am on a June morning in the countryside, leaving a house where the windows were open, and yet Mary Lowry heard nothing, and her mother in law, Rita Lowry heard nothing.

Mr Condon said Mary Lowry's evidence was the "baseline fuel" for the prosecution to get the train up the hill to a guilty verdict. She contextualised everything else but the problem was her evidence was not "gold standard".

Mr Condon will continue his speech to the jury tomorrow.