Man 'acted out of instinct' when he fatally stabbed man who 'trespassed' on his Dublin home

Alison O’Riordan

Murder accused Derek Boyd "acted out of instinct" when he fatally stabbed a man who "trespassed" on his north Dublin home and was entitled to protect himself if he was under attack, his lawyers have told a Central Criminal Court jury.

However, the prosecution said the accused man had chosen to pick up a knife in "a determined, murderous attack" and the deceased's return to the house "wasn't remotely threatening but entirely reasonable" as he was going back to "sort out" an earlier row.

Boyd took the stand at his trial on Thursday, telling a jury how he picked up a knife and "begged" the man he'd been drinking with just moments earlier to leave his home, only for the deceased to repeatedly threaten to kill him.

The accused man said that Mark Carroll grabbed him and, during a struggle, tried to take the knife.

Boyd said he managed to "break free" and swung the knife at least three times, but never intended to kill or seriously injure Carroll.

The jury has heard that Boyd was serving the suspended portion of his sentence for the manslaughter of his sister when he fatally stabbed Carroll.

In his closing speech on Friday, Sean Guerin SC, prosecuting, told the jurors that Mr Boyd knew exactly what happened inside his home that night but had run away to the UK instead of telling the truth.

Ultimately, Guerin said, this was a "horrible, pointless and meaningless" killing as both men had been on friendly terms that day.

Counsel said there was an attempt during the cross-examination of Megan Rock [the deceased's girlfriend] to associate the phrase "sorting out" with a "nefarious" meaning, such as to teach Mr Boyd a lesson.

Guerin suggested that "sorting out a row between friends" was not just an obvious explanation of what was meant by Mr Carroll, but an entirely reasonable one too.

The trial has heard Rock told a garda that, when she and her partner had left Boyd's house following an argument, Carroll asked her to wait on the street while he returned to the house to "sort it out".

Guerin said that maybe Mr Carroll should have knocked on the door and waited for it to be opened, but he submitted his return to the house "wasn't remotely threatening, it was entirely reasonable...Rock said Carroll was simply going back to sort out the row".

Furthermore, the barrister suggested it would be an "extraordinary feature" for a man intent on "murderous violence" to have walked past a knife at Mr Boyd's front door. "What does that tell you about Carroll's intent about returning to the accused's house?" he asked the jurors.

Mr Guerin said the test was whether the accused man honestly believed the force used was reasonable in the circumstances and that there were a number of key features in the case to test the honesty of that belief.

Counsel said Mr Boyd had not just fled the scene and the country but had not come back to Ireland for a year. "What does that tell you about his honest belief of what happened on the night".

The lawyer invited the jury to draw the conclusion that there had been no physical altercation. "Mr Boyd's account is not just one to be not believed, but is an entirely outlandish account," he said.

Counsel suggested that the account given in Boyd's statement that both men were aggressively speaking to each other for a number of minutes was much closer to the truth than the sworn evidence given by the accused man.

The barrister submitted that Boyd had given the panel an account of "a very vivid threat" when he took the stand.

Guerin said the accused man hadn't mentioned two crucial facts to gardaí when he gave his statement in 2025; namely, Carroll's express verbal threats to stab Boyd and the two of them eyeing up the knife.

He suggested Boyd had "beefed up" the words used by Carroll so the jury would accept the possibility that the accused was acting in real fear for his life.

Counsel said the evidence pointed to one conclusion only: that Carroll went calmly back to Mr Boyd's house to try and sort out the row.

He said a verbal encounter between the two men went on for a period of time and only came to an end when the accused man chose to pick up the knife and "used it in a way incapable of being explained other than a determined murderous attack" on the deceased.

In his closing address, defence counsel Brendan Grehan SC suggested that the jury acquit Mr Boyd of the offence of murder and an assault charge on Rock.

Grehan agreed with Guerin that this was a "pointless killing" but went further, calling it an "entirely motiveless killing" after a day of socialising in a convivial manner between men who considered themselves friends.

Counsel said it was the prosecution's case that the accused ran away and therefore he is guilty of murder.

He suggested that this did not follow and that Boyd had a suspended sentence hanging over him like the 'sword of Damocles', which would come swinging down and have him go back to prison.

Counsel argued that a person is entitled to defend themselves in the safety of their own home when someone comes inside who is not invited; "which Mr Carroll surely wasn't....that includes killing someone if that is your honest belief in terms of the situation you find yourself in".

"When they start to threaten you, or advance aggressively you are not obliged to turn away...you are entitled to defend yourself...you are entitled to act with a greater degree of elasticity and the law gives you greater latitude as long as you hold the belief that someone has trespassed on your property, which ultimately is what Mr Boyd's case is".

The biggest factor in the case, Grehan argued, was that this had happened in Boyd's kitchen well after midnight at a time when he had ejected, thrown out or ordered Carroll and Rock to leave his house.

He suggested to the jury that it was "highly illogical and unreasonable" for anyone to have objectively thought that tempers could have cooled within the four minutes of Carroll returning to the house, or that all would be OK for Carroll to walk into the kitchen without knocking on the front door.

Mr Grehan said it "clearly" wasn't the case that Mr Carroll was going back to make peace and he instead had gone back in with a purpose. He said Ms Rock knew the nature of "the conversation or the sorting out" and that is why she waited three doors down.

In summary, counsel said the accused man "acted out of instinct" and was entitled to protect himself if he was under attack.

Boyd (31), with an address at Scribblestown Place, Finglas in Dublin 11 has pleaded not guilty to murdering Mark Carroll (34) at his home on June 9th 2024.

Boyd has also pleaded not guilty that on the same occasion he assaulted Megan Rock, causing her harm.

Boyd's partner Chantelle Harcourt (34), of Primrose Grove, Darndale in Dublin 17 has pleaded not guilty on the same date at Blanchardstown Garda Station, in circumstances where another person had committed an arrestable offence, namely murder, and knowing or believing that person to be guilty of that offence or of some other arrestable offence, did without reasonable excuse an act with intent to impede the apprehension or prosecution of the said person.

In relation to Harcourt, Guerin said the prosecution case is that she had avoided telling the truth in her statement made to gardai at Blanchardstown Garda Station, when she clearly knew a serious assault offence had been committed by her partner.

Counsel said the core message Harcourt had conveyed to gardai was that nothing had happened in the house, which he said was obviously done to protect Boyd.

The prosecutor suggested to the jurors that there was ample evidence that both accused were guilty of the charges against them.

The trial continues on Monday before Judge Melanie Greally and a jury of seven men and five women