He had been released from prison in April 2019, and told not to go to Whanganui. But by September 2019 he had been moving between Manaia and Whanganui to visit Mackay-Pātea for six months.
On September 20 she had arranged for her two boys, aged 5 and 6, to stay with whānau so she and Ngatai could spend time together.
That evening the two got into an argument about what to do, Justice Grice said.
He strangled Mackay-Patea until she lost consciousness and then stomped on her head.
He then dragged her into another room and covered her with blankets. He took her eftpos card and went to buy alcohol, leaving her in the closed house and taking her car.
He drank with friends, returning to the house briefly the next day to take her cellphone, which he used to send texts to her family as if she was still alive.
He abandoned the car on September 26 and Mackay-Pātea's family reported her missing on September 30. Her body was found in her home in Lee St on October 3 and Ngatai was arrested the next day.
Justice Grice said the time of Mackay-Pātea's death was uncertain. An autopsy found she had been strangled, and her skull was fractured.
Three members of Mackay-Pātea's family made victim impact statements in court.
Her sister Debbie Matthews spoke of the family's pain at not being able to bury Mackay-Patea whole and how sickened they were at receiving text messages that were not from her.
Mackay-Pātea was a gentle and quiet person, she said. She had her own house and car, was devoted to her children and worked part-time as a kaiako at a kohanga reo.
Mackay-Pātea had been left alone in a cold house for much too long, her aunt Deborah Matthews-Pātea said. Her casket had to be closed and her children never got to see her body.
"We couldn't see her, we couldn't hold her, we couldn't even dress her."
Older sister Deshannon Matthews is now the guardian of the two children. They have changed from happy-go-lucky boys to being stand-offish and clingy, she said, and they did not want to go back to school after the death.
Crown prosecutor Michele Wilkinson-Smith said domestic violence was too common in Whanganui. Photo / Bevan Conley
Domestic violence is much too common in Whanganui, Crown prosecutor Michele Wilkinson-Smith told the court. Only six weeks ago she had appeared at another such murder.
Strangling cases are "almost our bread and butter", she said.
"Every young man who punches a woman or puts his hands around her throat risks being where this young man sits."
She saw nothing in Ngatai's reports that should excuse him from at least 16 years in prison. A long minimum non-parole period would also give Mackay-Pātea's family time to heal, she said.
Ngatai's counsel, Paul Keegan, said he had taken responsibility and offered no excuses for his behaviour. He didn't go to Mackay-Pātea's house with the intention of harming her, and the violence was brief, impulsive and without a weapon.
Ngatai was intelligent and only 26. Rehabilitation was possible, and he was motivated to make the most of his time in prison.
Exposure to "various forms of abuse" had affected his client.
"He says, through me, that he is filled with profound regret and he is deeply sorry - also for the appalling actions he took, leaving her cold and alone in her own home."
Ngatai had two previous convictions for violence, Grice said, with one incident before he was 18. He spent four years in prison for an incident where he threatened to cut the victim into pieces with a boning knife.
Mackay-Pātea was a vulnerable victim, she said, and should have been able to trust him. He had offered her no medical help after the violence, despite the fact she must have vomited at some stage.
The murder showed a high level of cruelty, brutality, depravity and callousness, Justice Grice said.
Reports said Ngatai he had been bright at Opunake High School, but used drugs early, fought and was expelled. His mother's family was supportive, but his father had been abused as a child in foster care and was in and out of prison.
Ngatai had been subjected to abuse himself, witnessed a family suicide and has felt suicidal himself.
He affiliates to Ngā Ruahine and Te Atihaunui ā Pāpārangi and after spending time in the Māori Focus Unit at Whanganui Prison he told the report writer he was "no longer a lost Māori boy".
He had recently spent time with his Kaiwhaiki grandfather, who told him about his people's loss of land.
"Systemic deprivation" as the result of colonisation is becoming increasingly familiar in the courts, Justice Grice said, and may have contributed to his offending.
She reduced his non-parole minimum to 15 years, because of his youth, his rehabilitation prospects, his mental health and his cultural issues.
He was also sentenced to 12 months' prison for taking the vehicle and three years' prison for the theft and document charges. All are to be served concurrently.
