Sean Guerin suggested that the cause of Mr Fitzpatrick’s death was self-impalement and that the jury would have to decide not if his stepson’s death was his fault, but if he bore criminal responsibility.
Mr Guerin spent much of yesterday giving his closing speech to the Central Criminal Court on behalf of the Dubliner charged with murdering the brother of missing teenager Amy Fitzpatrick.
Mr Mahon, aged 45, has pleaded not guilty to murdering the father of one on May 26, 2013.
The 23-year-old received a stab wound to the abdomen outside the apartment that his mother, Audrey Fitzpatrick, shared with Mr Mahon at Burnell Square, Northern Cross.
Mr Mahon said his stepson had pulled a knife on him and that he had wrestled it from him. He said he then took the knife out to show it to him and that Mr Fitzpatrick had walked onto it. The trial heard Mr Fitzpatrick ran downstairs, but collapsed and bled to death.
Mr Guerin noted that when asked by gardaí if he thought the death was his fault, Mr Mahon said he did. The barrister said that if his client had not taken the knife out when he did, his stepson would not have died.
“As he said himself, it was a very, very stupid thing to do. It had terribly tragic consequences,” said Mr Guerin. “David Mahon will have to live with the knowledge of his fault in the death for the rest of his life.”
He noted that prosecutor Remy Farrell had said in his opening speech that the science and post-mortem findings would be silent witnesses for the prosecution.
“It may be that the prosecution wishes the pathologist had remained silent,” he said.
He was referring to Dr Michael Curtis’s view that it was possible that Mr Fitzpatrick had walked onto the knife.
Mr Farrell had also told the jurors that they would not be able to reconcile Mr Mahon’s account with the scientific evidence.
“Dr Curtis had no difficulty reconciling Mr Mahon’s account with the science and he’s a scientist,” he said.
Mr Guerin said that, as if that was not enough, the prosecution had suggested that the deceased had been eviscerated, something the pathologist had rejected.
“That’s an exaggeration designed to disgust you, to portray David Mahon as some sort of butcher, some sort of savage, who had gutted Dean Fitzpatrick,” he said. “They tried to evoke in you this instinctive, emotive response, to turn you against him.”
Ms Justice Margaret Heneghan told the jury of six women and six men, that three possible verdicts would be open to them: Guilty; not guilty of murder but guilty of manslaughter; and not guilty.