A murder trial jury at the Central Criminal Court must consider whether a then 17-year-old boy used reasonable force when a fisherman came into his home in the early hours of the morning and was stabbed in the chest.
Mr Justice Paul McDermott told the seven women and four men that there are three verdicts available in the trial of Dean Kerrie, who denies murdering Jack Power.
He said they must first consider whether he honestly believed that Mr Power had entered his home as a trespasser intending to commit a criminal act. Secondly they must consider whether Mr Kerrie's use of force was necessary to protect himself or others from Mr Power or to prevent a criminal act.
The judge added: "If you find that in the circumstances faced by him, that he applied such force as was objectively reasonable in the circumstances, then he has acted in a lawful manner and is entitled to an acquittal."
If he used excessive force but had an honest belief that the force he used was necessary then he is not guilty of murder but guilty of manslaughter, the judge said. He added: "If you find that the accused knew the force used was excessive then you must find him guilty of murder."
The judge said that the evidence has come from a number of people with different recollections, presentations and accounts as to what happened. He said the build up to the stabbing was that Mr Power had been drinking in a pub with a number of people from about 9 or 10pm.
When Mr Power left the pub, the judge said he seemed to come to the conclusion that damage to his car had been caused by Mr Kerrie. He went to Mr Kerrie's home, took a rock from a flower bed and used it to smash one of the windows of Mr Kerrie's home before entering the house. He died a short time later from a single stab wound, the judge said.
He told the jury that the weight to be attached to any evidence or whether they consider a witness to be credible is a matter solely for them. He said: "You can accept all the testimony a witness gives or part of it, or you can reject it all or reject part or elements of it, that is a matter for you."
Mr Kerrie had also given an account to gardai which the jury must take on board, he said, but he said they can accept or reject any part of it as they deem appropriate. If they find that they don't accept something that Mr Kerrie said, the judge told them that does not mean they must convict. He added; "You have to stand back and consider all the evidence you have been furnished with. You must assess it and see whether the prosecution has proved its case beyond a reasonable doubt."
Dean Kerrie (20) with an address at St Brigid's Square, Portarlington in Co Laois has pleaded not guilty to murdering 25-year-old Jack Power at Shanakiel, Dunmore East, Co Waterford on July 26, 2018. The accused was 17 years old at the time.
The jury has heard a 999 call made by Mr Kerrie at 3.44am on July 26th, in which the teenager said that Mr Power had come "in the front door at him" and tried to hit him. He said he had stabbed Mr Power in the chest with a kitchen knife but that he didn't mean to.
Eyewitness Christopher Lee, however, has denied that his best friend, Mr Power, forcibly pushed in the front door of the Kerrie house that night and said these were "lies" Mr Kerrie had to make up "to get away with it". Mr Lee has told the trial that Mr Kerrie "deliberately killed" Mr Power.
In his closing speech, defence counsel Ciaran O'Loughlin SC said that Mr Kerrie had picked up the knife to try to "ward off" Mr Power but that the knife "unfortunately" went through "soft tissue" after a scuffle in the house resulting in "tragedy".
The jury began their deliberations on Tuesday and will return to the Central Criminal Court tomorrow.