A Dublin man has lost his Supreme Court appeal against the severity of a seven-year sentence for the manslaughter of his partner's son.
The court rejected David Mahon's appeal and said the introduction of a lethal instrument into an "emotional situation" was unjustifiable.
Mr Justice Peter Charleton said that absent an attack with deadly force and an action in self defence in extreme circumstances, there could never be an excuse for the production of a knife.
48-year-old David Mahon denied the murder of 23-year-old Dean Fitzpatrick in May 2013.
Mr Fitzpatrick was stabbed in the abdomen outside the apartment Mahon shared with Mr Fitzpatrick's mother, Audrey, at Northern Cross on the Malahide Road in Dublin.
Mahon was found guilty of manslaughter and sentenced to seven years in jail in June 2016.
Mr Justice Charleton's judgment has set out guidelines for sentencing judges in manslaughter cases where two paths to the same jury verdict may be possible.
He also stressed that attacks by men on women should be regarded with particular seriousness.
