The family of a slain Auckland shopkeeper say they relived the worst day of their lives countless times for nothing, after a teenager was cleared of murder.

After a day's deliberation in the High Court at Auckland, a jury yesterday found the 14-year-old boy guilty of the manslaughter of dairy owner Arun Kumar but not guilty of the more serious charge.

His 13-year-old co-accused was acquitted of manslaughter and embraced tearful family members in the public gallery while telling his friend "good luck, my bro".

The pair have name suppression until at least the end of the next month, when defence lawyers will apply for permanent non-publication orders.

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Outside court, the family of Mr Kumar spoke of their disgust at the outcome.

"The heart and soul of our family was taken away," the victim's son Shivneel Kumar said.

CCTV footage of the horrific incident, from inside the Railside Dairy on June 10 last year, was played regularly during the three-week trial.

"We endured countless reruns of my dad's last moments. We tolerated all this to obtain justice for my dad."

Shivneel, supported by his sobbing mother Anita, said they now felt that had been for nothing.

"We are now living in a society where kids are on drugs, roaming the streets with weapons at the ready," he said.

There was never any dispute that the 14-year-old caused the fatal wound to Mr Kumar when he stabbed him in the neck, or that his co-defendant was standing outside the shop with a metal pole.

But defence counsel spent much time detailing the boys' backgrounds and the psychologically debilitating effects they had on them.

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The court heard evidence that the older defendant suffered a severe head injury after being hit by a car six years ago.

The lack of rehabilitation and an addiction to synthetic cannabis resulted in a reduced capacity, particularly in "complex" situations.

The jury also heard details of the 13-year-old's troubled upbringing.

His lawyer, David Niven, said his client had a brain "like Swiss cheese" after his mother smoked methamphetamine and consumed alcohol while pregnant with him.

He had taken drugs and witnessed regular domestic violence, which contributed to his lower IQ and behavioural disorder.

Mr Niven told the court the boys' original idea was to break into a nearby shoe shop.

The change of plan to hit the dairy came at the eleventh hour and they would have had less than three minutes to plan the theft.

The Crown said the armed robbery might not have been well planned but each of the boys wanted money and had weapons to achieve their goal.

Prosecutor Kieran Raftery said the older boy had the knife concealed and "at the ready" and they must have known there was a reasonable possibility of violence.

However, the jury disagreed.

The 14-year-old was convicted of manslaughter and remanded in Child, Youth and Family (CYF) care by Justice Graham Lang.

He is one of about 10 children and it is understood his mother gave birth to her youngest child only weeks ago. A source close to the family said the children had a tough upbringing and most had spent time in CYF care.

The 14-year-old will be sentenced at the end of next month.NZME