Judge reveals Gemma O'Doherty used AI to prepare legal case as her appeal is dismissed

Ms Justice Caroline Costello said Ms O’Doherty used AI to prepare her written submissions that included 'hallucinations' of non-existent cases

Gemma O'Doherty (pictured) was seeking to strike out defamation proceedings brought against her by Jimmy Guerin, a councillor and brother of murdered journalist Veronica Guerin. File picture: Brian Lawless/PA

Litigants should inform their opponents and the court if they have used artificial intelligence (AI) to prepare their legal papers, the Court of Appeal has said, as it dismissed an appeal by activist Gemma O’Doherty citing authorities that “simply did not exist”.

Ms Justice Caroline Costello, writing for the three-judge court, said journalist Gemma O’Doherty, who did not have lawyers representing her, used AI to prepare her written submissions that included “hallucinations” of non-existent cases.

This is an “inherent and well-known risk” of using AI to write legal papers, the judge said, adding that parties are obliged not to mislead the court by advancing “fake” propositions that have no legal basis.

She said she does not believe Ms O’Doherty intended to mislead the court or was aware she was citing fictional cases. The judge noted there was then no guidance to help self-representing litigants know how they should and should not use AI in their cases.

Setting out a short set of principles on AI, the judge said litigants may use it responsibly to assist with research and should independently verify the accuracy of their submissions. 

It is “not acceptable” for parties to rely on cases they have not verified, and judges will be able to apply sanctions where AI leads to the court being misled.

Jimmy Guerin defamation

Ms Justice Costello made the comments as she rejected Ms O’Doherty’s appeal against the High Court’s refusal to strike out defamation proceedings brought against her by Jimmy Guerin, a councillor and brother of murdered journalist Veronica Guerin.

Gemma O’Doherty sought a strike out in December 2024, about a year after a jury failed to reach a verdict in the case following a five-day trial. Refusing her application, the High Court ordered a retrial, which has not yet occurred.

Mr Guerin claims Gemma O’Doherty, a former Irish Independent journalist, defamed him in social media posts and a website video from 2019 that, he alleges, conveyed he was a convicted paedophile. 

Posts by her said “paedophile brother of Veronica Guerin, murdered with the involvement of Garda” had been found guilty of possession of hundreds of child sexual abuse images”.

It was in fact Guerin’s brother, Martin Guerin (aged 73), who pleaded guilty in 2019 to possession of hundreds of images and 146 movie files of child sexual abuse material.

Jimmy Guerin claimed the words published were understood to refer to him. Gemma O’Doherty said her words were clearly intended and understood to refer to Martin Guerin.

In seeking a strike-out of the case, Ms O’Doherty alleged it was “malicious, vexatious, frivolous, based on fraud, perjury and deception”, a “grave attack on press freedom” and “bound to fail”. She has also brought a counterclaim for alleged defamation.

In her appeal she alleged, among other points, that the trial judge was objectively biased and her postings from July 2019 were made in the public interest and are protected by “absolute privilege”.

Court of Appeal ruling

In her judgment for the Court of Appeal, delivered this week, Ms Justuce Costello said O’Doherty needed to prove Guerin’s case disclosed no cause of action, was an abuse of process or bound to fail.

“It is not about ‘silencing’ the defendant or any journalist. Any person, including journalists, may properly be sued in defamation,” the judge said.

Costello found nothing in Guerin’s case amounted to an abuse of process. The High Court was correct to conclude that O’Doherty had “fallen well short” of establishing the claim was an abuse of process.

She said the case “undoubtedly” discloses a reasonable cause of action, while Gemma O’Doherty failed to provide a basis for suggesting the trial judge was objectively biased.

Ms Justice Costello, supported by Mr Justice Donald Binchy and Mr Justice Brian O’Moore, dismissed all eight grounds of appeal.