A Dublin man has lost an appeal against the severity of a seven-year sentence for killing his partner's son.

David Mahon (46) had pleaded not guilty to the murder of Dean Fitzpatrick (23), the older brother of missing teenager Amy, on May 26, 2013.

Dean Fitzpatrick received a stab wound to the abdomen outside the apartment his mother, Audrey Fitzpatrick, shared with David Mahon at Burnell Square, Northern Cross, on the Malahide Road in Dublin.

The two-week trial heard that Mahon had been in a relationship with Audrey Fitzpatrick for 12 years by the time her son died.

The State had argued that Mahon was drunk, angry and agitated when he thrust a knife into his stepson with deadly intent. Mahon claimed his death was an accident or possible suicide and that Mr Fitzpatrick had ‘walked into the knife’ while they had been arguing.

A Central Criminal Court jury found Mahon not guilty of murder but guilty of manslaughter and he was sentenced to seven years imprisonment by Ms Justice Margaret Heneghan on June 13, 2016.

The Court of Appeal upheld Mahon's sentence today.

Giving judgment in the three-judge court, Mr Justice George Birmingham said the sentence decided upon was not out of line with sentences in cases that might be regarded as broadly similar.

It was in the Court of Appeal's view, a sentence that fell within the range available and the appeal was dismissed.

Mr Justice Birmingham said that, as sentence appeal go, this one was “somewhat unusual”.

The case made on Mahon's behalf was that the Central Criminal Court judge did not sentence in accordance with the verdict of the jury.

The only thing that “one can say with certainty arising from the verdict is that jurors were not satisfied the prosecution had proved beyond reasonable doubt an intention to kill or cause serious injury”.

Opening an appeal against the severity of his sentence in October, Mahon's barrister, Seán Guerin SC, said there was no case “quite like this”.

He said Mahon was factually proven only to have produced the knife. That was all Mahon did, Mr Guerin said. He produced the knife, he didn't thrust it, he didn't stab, and because he didn't thrust it, he didn't commit an act that could have amounted to a physical assault.

Mr Guerin there were two distinct views open to the jury. The prosecution case for murder was that Mahon took out a knife and deliberately stabbed Mr Fitzpatrick causing his death.

The alternative view was that Mahon had merely produced the knife as if to show the victim “as it were”. He either intended to put him in fear or was reckless to put him in fear.

Mr Guerin said the only conclusion which could be drawn from the verdict is that the jury were not satisfied beyond a reasonable doubt that Mahon had stabbed the deceased.

Once that is acknowledged, Mr Guerin said it becomes clear that this was a “very unusual case” involving a “very low” level of culpability.

More to follow...