An out-of-work barman who stabbed his neighbour to death in "cold-blood" after an early-morning row over loud music has today been jailed for at least 10 years.

Tristan Ross Locke, 31, was found guilty of murdering neighbour Mark Graham Cowling, 44, on last Father's Day, September 6, 2020, after a trial at the High Court in Christchurch last month.

American-born Locke became so incensed with Cowling phoning noise control, and cutting power to his flat at least twice over a few hours, that he took a knife, went next door, and stabbed him to death, the trial heard.

Today, Locke was sentenced to life imprisonment with a minimum non-parole period of 10 years.

Cowling's father Graham, who lives in New Plymouth, says the impact of his son's murder in "cold-blood" has been overwhelming.

Mark Cowling was fatally stabbed by his neighbour Tristan Locke in Christchurch last September. (Photo / Supplied)

"Mark's death is, without comparison, the most distressing, heart-breaking and disgusting thing I've ever had to endure," he said in an emotional victim impact statement.

Since he was told his son had been killed, he's suffered a deep sadness and depression, which requires medication.

Cowling had moved to Christchurch six years ago to forge a new life.

He worked tirelessly and was well on his way to achieving his goal of his own home with his young family.

"I'm proud of what he had achieved," the devastated father said, sobbing in court this morning.

Cowling's mother Carol Cowling remembers a fun-loving, inquisitive, independent and caring son who had a large and loving heart.

Now, her joy in life has "dimmed" - nothing gives her the pleasure it once did.

Rebecca McMaster, Cowling's fiancé and mother of his young child, said the murder has torn their lives apart.

"I hate Tristan for what he has done to our family," said McMaster, who is now left scared, anxious and lonely.

McMaster went into survival mode after her partner's death, trying to stay strong for their child.

She wants to see Locke stay in prison for the rest of his life, not wanting him to ever be given the opportunity to destroy another family.

Crown prosecutor Barnaby Hawes highlighted Locke's "disproportionate response to what was really a trivial conflict".

But his lawyer, defence counsel Kirsten Gray said Locke's psychological make-up - he is on the autism spectrum disorder with a form of Asperger syndrome and antisocial personality disorder - was a contributing cause in the killing.

He'd felt frustrated and let down by the mental health system and probation services, unable to find his place in the world.

Justice Cameron Mander called the killing an "entirely senseless act".

The judge also highlighted Locke's previous convictions and propensity to arm himself when facing conflict, including in 2012 when he stabbed an associate in a fight, and approaching a noise control officer outside his house with a knife before the killing.

In sentencing Locke to life imprisonment with a minimum non-parole period of 10 years, Justice Mander stressed that life in prison "means just that" and that he will spend the rest of his life behind bars until the Parole Board is satisfied that he is no longer a risk to the community.

The trial heard that Cowling, his partner McMaster and young baby had been living in a block of five flats in the Christchurch suburb of Edgeware when Locke moved in last June.

Cowling's household, and other residents in the block, complained that Locke listened to music at high volumes, with the first noise complaint coming on July 9.

And from then, to the day father-of-three Cowling died, there had been a total of 21 noise complaints.

Noise control was called four times on the fateful night but the Crown said Locke would turn down the music when officials came to visit to avoid getting into trouble. Once they left, he'd turn it up again, the Crown claimed.

That night, a fed-up Cowling accessed the fuse box which serviced the whole block of flats and cut the power to Locke's house on at least two occasions.

On the final occasion, at 2.25am, Locke responded by taking a knife from his kitchen and went to Cowling's property.

The Crown said while it is not clear what unfolded, it says that Locke stabbed Cowling in the chest three times, causing a 10-12cm fatal wound that injured his heart and lung.

Cowling's partner woke to the sound of broken glass and came down to find Cowling on the laundry floor with Locke on top of him applying pressure to wounds with an old towel or jersey.

She asked Locke to leave but he refused and was allegedly acting aggressively.

Locke phoned 111 and he was arrested at the scene, with a knife found on the path outside.

Detective Michael Henderson-Rauter handled Locke while he was in custody, and informed him at 4.27am - less than two hours after the altercation – that Cowling had died from his injuries.

The police officer told the court that Locke responded by saying, "Oh wow, savage. F***".

Henderson-Rauter then arrested him for murder and read him his rights.

Asked if he understood that he was under arrest, Locke allegedly replied: "I'm going to be a New Zealand resident" and "I'm going to be here for a very long time."Locke told the police officer that he was intoxicated and had been for the last week.

Accompanying him on a toilet break, the detective noted Locke saying, "That guy didn't deserve it."

Locke later allegedly said he was "pretty screwed" and that he couldn't be "put to death in this country" which was "probably a good thing".

He later allegedly added: "How did I even do that? F****** stupid" and "Death row, do me a favour."