Tagger-killer Bruce Emery will walk free from prison less than two years after being convicted of fatally stabbing a teenage boy.

Last night, the Sensible Sentencing Trust welcomed his imminent release and said he should never have gone to jail - a view condemned as "disgraceful" by Green Party co-leader Metiria Turei.

Emery, a father of three, found Pihema Cameron and a friend vandalising the garage door of his Manurewa home.

He chased them 300m down the street armed with a knife, and during a confrontation stabbed the 15-year-old in the stomach.

Later, he said he acted in self-defence.

"I thought they were attacking me so I put the knife up against his shoulder as he came towards me. He more or less stepped into it," he told the jury at his trial in the High Court at Auckland in December 2008.

He was charged with murder, but was found guilty of manslaughter.

The case sparked debate over the rights of property owners to protect their homes.

But the verdict and prison term of four years and three months, imposed in February last year, outraged Pihema's family, who saw it as a lenient sentence.

Now, less than two years later, the Parole Board has decided to release the 52-year-old.

"The board is very much aware of the seriousness of the offence and the fact that it involved the loss of a human life," it said in its decision.

"It is not the role of the board to decide when an offender has served a sufficient period of his sentence."

The most important consideration in every case was the safety of the community, and the board believed Emery was not a risk to the public.

He was first eligible for parole in April, but the Parole Board had concerns over his mood and requested a psychologist's report.

"His mood has been stable for some time," the board said.

"Mr Emery has the support of his wife and his family and others of his church. While in prison it is clear that he has behaved appropriately and is minimum security."

Under the terms of his release, Emery is not allowed to visit the area of Manukau where the attack took place and is not allowed to contact the Cameron family.

He is also not return to his Mahia Rd family home.

Sensible Sentencing Trust head Garth McVicar - who usually backs the victims of crime - supported Emery's early release.

He said Emery had to "pay a price for what he did" but the 52-year-old was a "different type of offender".

"I didn't think he should have gone to jail," said Mr McVicar.

"That young offender [Pihema] had been doing graffiti before and Emery had been becoming extremely frustrated with it.

"This is an exceptional case, and I think the judge got it right. He treated it as an exceptional case, and the Parole Board did exactly the same."

Metiria Turei said Mr McVicar's attitude towards Pihema Cameron - as an offender rather than a victim - was disgraceful.

"Garth McVicar has used this case to suggest that vigilantism is the right course of action, and this young man deserved to be killed.

"He is clearly not committed to the rights of victims or their families, but chooses those victims and their families that he thinks are worthy," Ms Turei said.

The police officer in charge of the homicide inquiry, Detective Senior Sergeant Gary Lendrum, said Pihema Cameron was a "good kid".

"He had virtually never been in trouble with the police before that night. What he was doing that night was clearly wrong, but did he deserve to be stabbed for it?"

Emery's lawyer at his trial, Chris Comeskey, said he was glad that his former client was to be released.

"He's done his time ... He's an extremely decent bloke and I just hope him and his family can move on."

Pihema's mother, Leanne Cameron, moved to Australia after her son's death.