It was a moment of rage, fuelled by alcohol, that led to a tragedy nobody thought would happen if they were sober, he said.
"The family has lost in effect two sons."
Mansfield tried to displace the mandatory life imprisonment sentence as manifestly unjust.
However, Crown submissions maintained that the sentence was required by law.
Crown prosecutor Alysha McClintock said the case did not reach the "very high threshold" where it would be manifestly unjust to impose the sentence Parliament presumed would be applied.
One witness said when he returned Marino was apologising and seemed to be trying to calm things down, the court heard.
However, Peter stabbed his brother in the chest causing an 11cm deep wound that pierced his heart.
In a later police interview, he said he not recall this moment and only intended to scare him.
The court heard, he immediately threw the knife down on the grass and tried to help his dying brother.
Further efforts to resuscitate him made by others were unsuccessful.
Peter walked down the street where a family member joined him and they waited together until police arrived, the court heard.
Peter James Te Maru was sentenced today in the High Court at Auckland. Photo / File
A blood test taken some hours after the stabbing, showed the defendant had 13 milligrams of alcohol per 100 millilitres of blood in his system.
This is lower than the threshold for legally driving in New Zealand.
"While it is likely your alcohol level was higher than this at the time of the stabbing, there was no suggestion that you were so intoxicated to the point you could not act of your own volition," Justice Fitzgerald said.
In sentencing, the judge considered the complex relationship between the brothers and the factors personal to the defendant.
"Your grandparents raised you in South Auckland and while then you may have preferred to be with your immediate family, you now believe it was the best thing for you," she said.
After the death of his grandmother, Peter moved to the Hokianga area in Northland where he enjoyed hunting and fishing.
He excelled in rugby, later playing representative rugby for the region.
At 18, he joined family in Queensland with the hope of making a career in rugby league but recurring injuries meant this was not to be.
He was deported back to New Zealand in 2017 due to convictions in Australia.
The court heard he had always managed to maintain steady employment.
While the defendant believed he was guilty of manslaughter rather than murder, the judge did not believe this detracted from his remorse.
"You are clearly aware that the consequences of what happened are felt by not only you, but also your family," Justice Fitzgerald said.
"The insight you show into the factors which contributed to your offending is encouraging, as is your obvious willingness to address them."
Justice Fitzgerald said the 34-year-old man was genuinely remorseful and had good rehabilitation prospects, before handing down the life sentence.
Peter Te Maru was given a minimum non-parole period of 10 years, with the judge saying it may well be that after that time the Parole Board could release him.