The heartbroken family of the woman brutally bashed by her boyfriend before he left her to die have applauded his 20-year life sentence and hope he stays behind bars for even longer.

Dylyn Mitchell Davis, 26, avoided life imprisonment without parole despite being issued his third strike and was sentenced at the Hamilton High Court today to a minimum 20 years in jail for the murder of Aroha Kerehoma.

Justice Paul Davison ruled life sentence without parole was manifestly unjust taking into account a number of factors including comparable cases where the cruelty, callousness and brutality was higher, and Davis' young age.

Given the average life expectancy, a life sentence without parole would mean he would be in jail three times longer if the three strike regime was applied.

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However, Justice Davison believed a life sentence of a minimum 20 years - the second option under the three strikes rule - was just, because of the brutal attack, lack of remorse and high likelihood of reoffending.

It was an appropriate sentence to punish Davis and a necessary means to protect the public, he said.

"Your attack on Aroha was cowardly. You were much stronger than her and the ferocity of your punches to her head would have instantly prevented her from taking any action to avoid assault."

The public would not tolerate domestic violence on women, he said.

The seats in the High Court were crowded with family and friends of Kerehoma, many wearing T-shirts emblazoned with the words "Justice for Aroha", who cheered and yelled at Davis when the sentence was given.

Outside the court, Kerohoma's aunt Judi Waugh said they had hoped for more, but were happy with 20 years.

"I'm pretty sure he will stuff up in jail and give himself more, but he deserves more.

"It's lifted a little bit of weight off my sister's shoulders, but she's still got a life sentence without Aroha. We all have a life sentence without Aroha."

During the sentencing, defence lawyer Thomas Sutcliffe said the murder was not the worst imaginable and an appropriate sentence would be 11 years. He argued life imprisonment without parole was manifestly unjust.

But Crown prosecutor Ross Douch, QC, said the offence was high level because of the callousness, cruelty and brutality involved in the attack. Davis repeatedly bashed Kerehoma on the head and face and then left her to die. He said Davis should be sentenced to life imprisonment without parole.

Kerehoma's mother Luana Kerehoma, in a victim statement read by Aroha's aunt, said her world had come crashing down when she learned her daughter had been killed, and called Davis "pure evil".

Davis' brutal actions meant her other children had lost their innocence because they now knew what evil was, she said. "My children are hurting and miss their big sister every day."

She said her loving and strong daughter had her whole life in front of her and had dreams of settling down, having a baby and buying a sewing machine so she could make gowns.

Victim impact statements were also read by two of Aroha's sisters, her grandmother, aunt and cousin who told how their hearts had been broken over her death.

"If I had one thing to say to the person who did this to you it would be, I hate you more than anything else in this world and I pray to God that you get what you deserve," her sister told the court.

Another sister, who had trouble sleeping at night because she was thinking about her older sister, said Davis had told her he would never hit Aroha and then he killed her.

"I will never forgive you for causing us so much pain. I will forever miss her smile, her laugh, our time we spent together."

On the afternoon before her death Davis and Kerehoma had been drinking and playing music in their garage.

She began texting her ex-partner later in the evening saying she did not feel safe because Davis had been hitting her.

She sent her last text message at 11.58pm on February 3 before Davis took the phone from her and began his assault. He then changed his clothes and left her to die in the garage.

He went to an associate's house and told her how he had bashed Kerehoma and that she "had it coming". He then told another associate he had killed her and that he had "choked the bitch".

He returned home more than 12 hours later and called an ambulance. When medics arrived, they said it appeared she had been dead for hours. It could not be ruled out that she may have survived if an ambulance had been called earlier.

A post-mortem examination found no weapons were used in the attack and that Kerehoma's horrific head injuries, which caused her death were consistent with the use of fists. The shocking injuries included a bashed nasal bone, fractures in the base of her skull and extensive bruises to her face.

Davis initially denied the murder, but later pleaded guilty.

Davis' first strike was for wounding with intent to injure in 2014 and his second strike was for aggravated robbery in 2015.

Sensible Sentencing Trust founder Garth McVicar today said the decision not to sentence Davis to life without parole was outrageous and judges were not making the full use of the tools given to them in 2010. He called on the Crown to appeal the sentence.

"Parliament was very clear when the three strikes law was passed in 2010, that murderers with prior strike convictions are expected to receive the ultimate penalty - a sentence of life without parole."

Man admits murder of Hamilton woman Aroha Kerehoma