Lawyers for convicted murderer Graham Dwyer have argued that a verdict of not guilty should have been directed at his trial, because the possibility that his victim, Elaine O'Hara, had taken her own life could not be excluded.

The Appeal Court has begun hearing Dwyer’s appeal against his conviction more than seven years ago for Ms O’Hara’s murder, following his successful challenge to the legislation used to retain and access his mobile phone data.

Dwyer was found guilty by a jury in March 2015 of the murder of Ms O’Hara, 36, after a trial containing evidence described by the Appeal Court president as "truly shocking".

Mobile phone data linking his work phone to other phones and text messages formed part of the evidence against him in what his lawyers said was an intrinsic part of the prosecution case.

Dwyer successfully challenged the Irish legislation under which this data was retained and accessed, all the way to the European Court of Justice and the Supreme Court.

Senior Counsel Remy Farrell said the European Court had repeatedly ruled that a system of general and indiscriminate retention of mobile phone data for law enforcement purposes was simply not allowed.

There may be misgivings about those rulings he said, because of their huge implications for law enforcement, but they couldn’t be ignored.

He said it was "highly problematic" that the Irish courts continued to question the logic underpinning the ECJ’s decisions on this matter.

Mr Farrell said they were not arguing the mobile phone evidence should automatically be excluded in Dwyer’s case. But he said his client wanted a retrial where a test would be applied to decide if it could be admitted.

We need your consent to load this rte-player contentWe use rte-player to manage extra content that can set cookies on your device and collect data about your activity. Please review their details and accept them to load the content.Manage Preferences

A Supreme Court decision handed down after Dwyer's trial had found that evidence can be admitted even if a person’s rights are breached, as long as the breach was inadvertent or in good faith.

Mr Farrell argued that the evidence in Dwyer’s case was collected under a system that could never have been permissible.

The court was told Irish legislation allowed one’s mobile to be turned into a tracking device and the entire population to be put under surveillance.

Mr Farrell said Dwyer’s case was a particularly important case study. He was not someone who was under suspicion at the time his phone data was retained. But gardaí got his phone records going back as far as they could, from October 2011 to November 2012, and built up an intensely detailed picture of every part of his life, including his work, his home, his relationships, recreation, movement and activity.

Mr Farrell said Dwyer was literally monitored when he was at home.

He said Dwyer’s work phone was used as a "baseline" to attribute other phones to him and the prosecution also tied the data to the content of text messages. Mr Farrell said the prosecution was now describing the phone data as "merely supportive" of other evidence.

He said this was an attempt not just to unscramble the egg, but the entire omelette.

Senior Counsel Michael Bowman, also acting for Dwyer, raised the issue of explicit video clips, some featuring Dwyer and Ms O’Hara which he said should not have been shown to the jury.

Mr Bowman said these videos containing extreme material could have been dealt with by means of giving verbal evidence about what was in them instead of showing them in court. He said there was a very clear risk that they had the capacity to overwhelm the jury and compromise Dwyer’s right to a fair trial and his presumption of innocence.

He also raised an allegation that the trial judge Mr Justice Tony Hunt had glared at Dwyer and shaken his head during evidence which was being given about a map.

Appeal court president, George Birmingham said some of the evidence in the case was by any standards "truly shocking" and it would be hard to sit through eight weeks without showing any emotion, but he found it surprising that a map would produce this reaction.

Mr Bowman also criticised some media reports and social media commentary about the case, saying Dwyer was dealing with a hostile, negative environment within the court and outside it. Mr Bowman said the cumulative effect of all these matters caused them concern.

Finally, Dwyer’s lawyers submitted that there was no evidence about Ms O’Hara’s cause of death and no forensic evidence to support the prosecution case that she had died by stabbing. Mr Bowman said the issue of suicide remained live and large within the case and the correct approach of the trial judge should have been to direct a verdict of not guilty.

Lawyers for the DPP will respond tomorrow, after which it’s likely the three appeal court judges will reserve their decision.

Dwyer was in court for the appeal, dressed in a black suit and tie and white shirt.

Elaine O’Hara’s father and other family members were in court as well as Dwyer’s father and sister.