The boy accused of murdering west Auckland dairy owner Arun Kumar came from a violent home where drugs were sold and the children were left to look after each other, a jury has been told.
The boy, who is now 14, has name suppression, as does a 13-year-old who is charged with manslaughter over Mr Kumar's death. Both are also charged with assault with intent to rob.
Details of the 14-year-old's background were revealed at the High Court in Auckland today, where the boy's brother and a medical expert gave evidence.
Neuropsychologist Valerie McGinn went through the boy's school and social welfare records as part of her analysis.
She said they told a story of neglect and suffering, and at least 20 notifications to Child Youth and Family from neighbours and teachers concerned about the safety of the boy and his siblings.
Ten of the notifications were for family violence. In 2004 alone there were three investigations by social workers who found the younger children were often being looked after by their siblings, then aged 12 and 13.
The following year the children's mother dropped them off with a relative and did not return for three weeks.
An investigation found she had been using methamphetamine and heroin and shooting up in front of the children.
Boy hit by car
Dr McGinn said she believed the boy suffered brain damage when he was nine years old. He was hit by a car going 50km an hour while using a pedestrian crossing, thrown 4 metres and left with a fractured skull.
She said an adult with the same injury would be off work for two years but this boy was sent back to school after two weeks.
The school raised concerns after the boy spoke of suicide. On another ocasion he repeatedly banged his head on a classroom wall and when a teacher asked him why, he said he didn't want to feel anymore.
The school referred him to a specialist clinic where he was eventually seen, but the clinic concluded there were no longer any concerns.
Dr McGinn said that was impossible, given the boy's injury.
Tests showed brain damage
She put the boy through a range of tests, some of which showed he had ongoing brain damage.
In one of them he scored at a similar rate to a six-year-old.
However Dr McGinn said the boy knew right from wrong. She confirmed under cross-examination that he knew it was wrong to rob and kill people.
But she said in a complex situation, he would act on impulse, without thought.
The court also heard the boy was addicted to drugs.
His brother spoke of him being hooked on synthetic cannabis and looking like a zombie. He said his mother tried to get the boy off synthetic cannabis by giving him the real thing.
He said people sold drugs from the family home and he moved out when he was old enough to realise what was happening.