The defence in the 'Mr Moonlight' trial was prejudiced by "side issues" and remarks about "who was going to be smelling somebody else's knickers", the Court of Appeal has been told.
Lawyers for killer Patrick Quirke claim the trial judge gave too much leeway to the prosecution and let evidence be admitted even though it was unproven or of little or no value as evidence.
They also complained the defence team was put on the back foot by the repeated late disclosure of evidence to them as the trial progressed.
These were among 52 grounds of appeal being advanced as they seek to overturn Quirke's conviction for the murder of love rival Bobby Ryan in 2011.
His counsel, Bernard Condon SC, said the approach adopted by trial judge Ms Justice Eileen Creedon and the prosecution had led to "enormous dollops of prejudice" being heaped on his client.
He argued irrelevant and prejudicial material went before the jury. This included evidence from his former lover Mary Lowry, in which she alleged Quirke stole knickers from her clothes line.
According to Mr Condon, Ms Lowry was an "extraordinarily compromised witness" who was bitter towards Quirke and gave inconsistent and unreliable evidence.
Married farmer Quirke (51), of Breanshamore, Co Tipperary, was jailed for life last year after a trial which gripped the nation for 13 weeks.
The prosecution alleged he carried out the murder so he could rekindle an affair with Ms Lowry, who was in a relationship with Mr Ryan at the time. Mr Ryan disappeared on June 3, 2011, after spending the night at Ms Lowry's home at Fawnagown, Co Tipperary. His body lay undiscovered in a run-off tank for two years.
Mr Condon said Ms Lowry was an important witness for the prosecution and accounted for 115 pages in the book of evidence. He said before the trial he identified portions of 40 of these pages that he believed should not be put before the jury for a variety of reasons.
Some of the passages were irrelevant, some lacked an evidential basis and some were more prejudicial than probative, Ms Condon claimed.
While the trial judge ruled out some of the matters identified, she left in others, despite objections from the defence.
Mr Condon said part of his reason for seeking to limit the material put to the jury was so the case would not "degenerate into a family law dispute".
He said adult relationships could break down and were often accompanied by feelings of bitterness. In these circumstances, care needed to be exercised so that a line wasn't crossed where the relationship breakdown became the focus of the jury, he said.
He said the prosecution could have limited the chance of prejudice occurring.
"Instead of which, a very large amount of sub issues and side issues and sniffing underwear on clothes lines and who was going to be smelling somebody else's knickers were admitted, over my objections," he said.
Mr Condon said evidence from Ms Lowry that Quirke was acting strangely at his son's confirmation was also prejudicial, while evidence of financial arrangements between Quirke and Ms Lowry were allowed go before the jury even though they were not proved. He also claimed references to Quirke being depressed were "very stigmatising, unfortunately". Mr Condon said gardaí made prejudicial comments during interviews with Quirke that should not have been heard by the jury. This included a comment by a garda that Quirke had "cash on demand and sex on demand" from Ms Lowry.
He said "tittle tattle" about "who looked crooked at who" at a birthday party and a confirmation party also became part of the case.
The appeal, before Mr Justice George Birmingham, Mr Justice Patrick McCarthy and Ms Justice Isobel Kennedy, is being conducted remotely due to the pandemic and could last for four days.
Quirke watched the hearing via a video link from prison.