A father who kicked and beat his 5-year-old son to death has lost an appeal to get his prison sentence reduced.

William James Sio appealed his 17-year minimum prison sentence for the murder of his son Ferro-James Sio. The decision on this appeal was released today.

Sio, who was 25 when he was sentenced last year, admitted five charges, including murdering his son on February 8, 2020, at a Union St emergency housing property in Rotorua.

Ferro-James Sio. Photo / Supplied

Sio also pleaded guilty to two joint charges with his partner, Leza Rawiri, of ill-treating and neglecting Ferro-James, assaulting the child and failing to get medical care for him after he stopped breathing.

Rawiri, 29, has been jailed for five years and seven months.

A summary of facts revealed details of the abuse at the hands of Sio and Rawiri confirmed the little boy died after a sustained beating.

Sio admitted to police he did it and said he felt stressed as he had to "find a house and do everything else" and he was "not the parent of the year".

Sio would become frustrated by what he thought was bad behaviour by Ferro-James.

He would make the boy face a wall with his hands out straight in front of him for long periods as punishment and would kick and hit him if he faltered.

On the night of his death, Sio kicked his son violently multiple times when he could no longer stand with his hands out. One kick was of such force, Ferro-James' breathing became shallow.

The summary said Sio told police he did CPR on his son and he began breathing again. He then lay down and went to sleep next to Rawiri, who told the police she was asleep during this time.

A few hours later, Sio told police he woke and found Ferro-James was cold and did not appear to be breathing. He tried to breathe into his son's mouth but without success.

Just before 10.30pm, Sio's phone was used to find a defibrillator nearby. A short time after this Rawiri went outside and had a cigarette.

About 10.50pm the pair took Ferro-James to Rotorua Hospital but he was already dead.

The appeal, heard by Justice Patricia Courtney, Justice Susan Thomas and Justice Mark Woolford in the Court of Appeal in Auckland on June 9, said Ferro-James was living in violent surroundings and no one did anything about it, despite there being concerns.

"The sad reality is that Mr Sio was totally ill-equipped to have sole custody of
his son," the judges said, in the decision.

They said Sio and Rawiri were violent towards each other and Sio and neither stopped each other's treatment of the child.

"Friends and associates of Mr Sio were obviously concerned about Mr Sio's treatment of his son. Unfortunately, it does not appear that anyone reported their concerns to the authorities."

The judges said they were satisfied the case fell "squarely" within the scope of the legislative policy that murders with the features of this case were sufficiently serious to justify a non-parole period of 17 years.

They said the fact Sio had a troubled upbringing and might have been kicked in the buttocks as a child did not bear any correlation to his behaviour towards his son.

"The level of violence was at an entirely different and fatal level. We also do not accept that it can be properly categorised as excessive discipline. It was gratuitous violence."

Details about the case revealed in court showed Sio was in a relationship with Ferro-James' mother but they separated in October 2014 just before Ferro-James turned 1.

Initially, Ferro-James was in his mother's care before Sio took full custody in 2017. In 2018, Sio started a relationship with Rawiri and it was described as "volatile" and "violent".

Ferro-James was found to have bruising and "pinch-type" marks on his body by his teacher at a Tauranga kohanga reo. The boy told a kohanga teacher that "aunty" - as he called Rawiri - had done it.

Sio worked as a bricklayer and sometimes he would take his son to work and the child would sit in the car the whole time. Sio often left Ferro-James with friends, sometimes for days.

William James Sio at an earlier High Court appearance. Photo / Andrew Warner

Sio did not enrol his son into school when he turned 5 so Sio's friends enrolled Ferro-James themselves at Ōwhata Primary School, where he started in October 2019.

It was Sio's associates who took him to school, gave him school supplies and helped with his homework.

In late January, Sio was staying with some friends in Rotorua when he punched Ferro-James hard in the chest and stomach, sending him flying backwards and into a hallway.

On January 24, Sio arranged to move into emergency housing on Union St in Rotorua with his son. Rawiri would also stay at the address, which was a small and cramped room with limited space to move around.

The pair often kept the room door closed and curtains pulled and had little interaction with other residents.

In the two weeks leading up to Ferro-James' death, residents heard the pair argue and fight daily.

Residents would hear Ferro-James screaming in a "frantic and distressed manner", hitting sounds and the boy crying.