A jury has been told that what David Mahon did in the aftermath of his stepson receiving a fatal stab wound was “straight out of the ‘how to get away with murder’ handbook”.

The prosecutor also said that, if it was a case of accident or suicide, Mr Mahon was the most unfortunate man in Ireland, who had given a good impression of someone who had committed murder.

Remy Farrell SC was giving his closing speech Friday morning in the trial, where the Dubliner is charged with murdering his stepson, Dean Fitzpatrick, who was the brother of missing teenager Amy Fitzpatrick.

The 45-year-old has pleaded not guilty to murdering the father of one on May 26th, 2013, a day after the deceased interfered with his bicycle to annoy him.

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. The Central Criminal Court has heard that he bled to death internally.

The court heard that the accused voiced the possibility to gardaí that Dean Fitzpatrick had walked into the knife he was holding on purpose.

Mr Farrell noted that the accused had not mentioned the possibility of suicide or any “terrible accident” to the friend with whom he had spent the following hours.

“That’s something he cooks up later for the gardaí,” said the barrister.

He said that Mr Mahon had, instead, fled the scene.

“David Mahon gives a very good impersonation of someone who has committed murder,” he said.

Mr Farrell asked the jurors to look at the “remarkable” number of lies that he said the accused had told gardai and to question the reason for each one.

“You’ll be satisfied they point to guilt,” he said.

He drew their attention to Mr Mahon’s explanation for persistently phoning his stepson that night. He told gardaí that it was for a chat and “to get sense into him”.

The lawyer asked the jurors if there was even one of them who believed that.

“He didn’t get sense into him. He got a knife into him actually,” he said.

He moved on to Mr Mahon’s account that Mr Fitzpatrick had pulled a knife on him in his apartment, but that he had wrestled it from him and put it in his back pocket, and that the deceased had left.

“A back pocket is rather a good place to put a knife if, a, you want to conceal it and, b, you want easy access,” he said.

Mr Farrell described Mr Mahon’s account of why he followed his stepson out of the apartment and took out the knife as “perhaps one of the most laughable parts” of his story.

“I thought we were half getting through to him,” he told gardaí. “I took the knife out to visualise to him, to ask him: ‘what are you doing pulling a knife on your auld fella?’”

“It seems, when chastising your stepson, that the point where you’re getting through to him is the point it might be a good time to pull out a knife,” remarked Mr Farrell, describing this as absurd and ridiculous.

He drew the jury’s attention to the pathological evidence that the wound was horizontal and that the knife would have been held tensely.

“Maybe he was showing Dean not just what a knife looked like, but what it looks like when you’re about to stab someone,” he added.

He said that the biggest lie the accused told was about the seriousness of the injury. Mr Mahon had told gardaí that he thought the knife had just nicked or grazed his stepson.

Mr Farrell said his fleeing the scene and his telling his friend that he thought the knife had gone right through suggested that he knew the extent of the injury. He also noted that the knife had hit the spine and left a groove.

“When you stick a knife into meat, you know when you hit bone,” he said, apologising for the analogy. “It must be a shocking feeling.”

Mr Farrell then moved to what he described as “the coldest, most calculated lie to cover up the most shameful part of his action”. He was referring to Mr Mahon giving the same explanation for not calling an ambulance.

“He made sure he wasn’t going to expose himself any further by making a 999 call. That would have got in the way of his plans to get away with it,” he said.

Instead, said the barrister, he fled the scene and threw away the knife.

“This is straight out of the ‘how to get away with murder’ handbook,” he said. “Disposing of a murder weapon is Murder 101.”

He asked the jury to consider the image of Mr Fitzpatrick lying on the ground in the company of strangers, “attempting to splutter his last words through blood”.

“He left him to die on the street,” he said.

“Contrast that image with David Mahon speeding away on the back roads of North Dublin, avoiding CCTV, throwing the knife away, apparently gagging for a drink,” he said, referring to Mr Mahon going for a pint in the following hours.

“A person’s immediate reaction to an incident is probably most telling,” he suggested.

“If this is a case of accident/suicide, there’s no question but that David Mahon is the most unfortunate man in Ireland,” he said.

“A confluence of unfortunate events put him in the wrong place at the wrong time holding a knife. He threatens to stab Dean that day. He threatens his (Mr Fitzpatrick’s) girlfriend with violence that night.”

He said that it was also unfortunate that Dean Fitzpatrick had pulled a knife on him and that it wasn’t witnessed by his friend, who was there.

“Perhaps most unfortunate is finding himself standing outside the apartment holding the knife, holding it braced, tense and ready for use. It’s getting beyond unfortunate. It’s getting tragic for David Mahon,” he continued.

“And at that moment, Dean Fitzpatrick decided to step onto the blade with sufficient force that it goes all the way through.”

He said the reality was that Mr Mahon was drunk, angry and agitated when he walked out of his apartment for a confrontation.

“In a moment of anger... he stabbed his stepson with deadly intent,” he said. “You will have no hesitation in finding him guilty of murder.”

The defence will deliver its closing speech on Tuesday before Ms Justice Margaret Heneghan and a jury of six women and six men.