The man at the centre of a 22-hour siege near Kawerau, where a police constable was shot in the head and three fellow officers were seriously injured, walked out halfway through his high court sentencing.

Rhys Richard Ngahiwi Warren, 28, was found guilty of six charges including attempted murder, wounding with intent to cause grievous bodily harm, and using a firearm against a law enforcement officer.

Justice Timothy Brewer sentenced Warren to preventative detention and a minimum of 10 years' imprisonment.

A heavy police and security presence was felt throughout the packed public gallery as victims of Warren's actions told the court how they feared for their lives and had their children's innocence stolen from them.

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However, a defiant Warren told the court that "None of this would have happened if they did not breach my rights", moments before walking out halfway through his sentencing.

The siege began about 10am on March 9, 2016, after gunshots were fired at a police plane above Onepu Springs Rd.

Warren injured four police officers as they surrounded and approached him at his grandmother's house on Onepu Springs Rd.

"Being a hunter and gatherer, I could have easily killed those officers in my house if I wanted to but that was not my intention," Warren said.

Constable Regan Mauheni was shot in the head and needed brain surgery plus shrapnel removed from different parts of his face, neck and chest.

"From the moment I was shot there was doubt from my colleagues and myself that I was going to live," he told the court.

"I went from being what a 30-year-old should be, independent and self-sufficient, to needing assistance in every aspect of my life."

Sergeant Logan Marsh was shot in the finger and required reconstructive surgery.

"On that day he stole my children's innocence and for that, I will not be forgiving," Mr Marsh said.

"From when I leave the house to go to work my kids are concerned I am not going to come home."

Constable Andrew Flinn, who suffered multiple wounds to his knee after being shot during the incident, said he was in no doubt Warren "intended to kill me and my team that day".

"My wife and children were understandably scared by the incident ... my wife will not sleep until I return home from work."

Warren repeatedly interrupted court to ask Justice Brewer to read from an affidavit the court had not yet received.

"Before all of this carry on I was at home living in peace with my loved ones, I was not bothering anyone," Justice Brewer read.

"The NZ Police invaded my home while I was sleeping. I was outnumbered and outgunned.

"Every man has the right to protect his whare [house], family and his castle."

Justice Brewer said Warren did not give police any sign of his presence on March 9, 2016.

"They broke several windows to see inside and they made voice appeals," Justice Brewer said. "You stayed hidden and silent."

Warren was armed with an ex-Army .303 bolt action rifle which he used to fire at one officer's head.

"He was so close to you that you could have reached out and touched him. When you fired, you intended to kill the officer."

Bullet fragments also struck the head of Mr Mauheni, who was following close behind.

Mr Mauheni dropped to the floor unconscious and a fellow officer used his body to shield him.

Mr Flinn began firing through the walls and Warren fired two more shots down the hallway, which struck a door frame and the bullet fragments hit him in the leg.

Warren picked up a police Glock pistol - dropped during the evacuation of the house - and fired it at Mr Marsh through a window, nearly killing him.

"The bullet passed through his palm and instead of striking him in the neck or chest
was stopped by the forward edge of the rifle magazine," Justice Brewer said.

Eventually, Warren was coerced into giving himself up after talking to Inspector Warwick Morehu, who knew Warren's family from his time stationed at Kawerau.

Justice Brewer said Warren had indications of paranoia and conspiracy ideation and doubted he would work with rehabilitative programmes.

A sentence of preventive detention was the best incentive for Warren to engage successfully in treatment, Justice Brewer said.