A Hamilton jury has been sent out to begin its deliberations as to whether two teen girls are guilty of the murder of a 54-year-old man.

Norman Kingi died after being stabbed in the heart by the older of two accused - aged 16 - after he and his partner, Vicki Reihana, busted them breaking into their car on Ranui St in July last year.

A second girl, now aged 14, also faces a murder charge. However her lawyer, Roger Laybourn, submitted she was standing about 2m away at the time the stabbing occurred.

Lawyer for the older accused Ron Mansfield said his client admitted stabbing Kingi but said it was an instinctive reaction out of self defence to an advancing, drunk and angry Kingi who was annoyed they had tried to steal his car.

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Justice Timothy Brewer spent just under two hours this morning summing up the case for the jury of five men and seven women.

They were sent out to begin their deliberations at midday.

A key issue in their deliberations was the issue of self defence, given it was the defence of the older accused who admits stabbing Kingi.

He told the jury they had to put themselves in the shoes of the accused and whether she was justified in stabbing Kingi.

Not only that, if they did find it was a justified action, they then had to decide whether the degree of force was reasonable given the circumstances the accused believed them to be.

The defence submitted that she felt Kingi was a threat – he was drunk, angry and advancing on her and her instinctive reaction to protect herself was to pull out the knife and stab him.

However, the Crown said the accused's actions were not reasonable and Kingi was simply in her way when she tried to rescue her friend so stabbed him out of anger, rather than fear.

The older accused had options that night, including running away either before or after the younger accused hit Kingi on the head with a screwdriver or pulled the knife and simply threatened him with it, rather than plunging it into his chest.

As for what was a reasonable amount of force, that could only be decided by the jury.

"It's not whether the defendant thought they were using reasonable force, it's whether the jury thinks the force is reasonable."

He also advised them of the difference between murder and manslaughter, and that as the older accused had admitted killing Kingi, which is an unlawful act, then she would be guilty of manslaughter.

However, if they found she was not justified in stabbing Kingi and the level of force was not reasonable, she should be found guilty of murder.

He added that the murder did not have to be pre-meditated and planned.

If they found that she knew using the knife would cause bodily injury, likely to cause death, and she was reckless as to whether he died or not, that would also be murder.

It could also be murder if someone suffered a serious injury which culminated in death while an offender was committing an offence, despite that not being their intention.

As for the younger accused, they had to be satisfied that she formed a "common intention" with her co-accused in going to rescue the 12-year-old, knowing that death or serious injury would be a probably consequence. If not, she should be not guilty.

She was charged as a party to murder, so her guilt would only be assessed if the jury were satisfied her co-accused was guilty of either murder or manslaughter.

An added clause had to be taken into account when considering her charge, given she is aged under 14, and that was she knew by forming the intention that she knew it was "wrong or contrary to the law".

Yesterday, Mansfield said his client never had any intention to carry a knife let alone stab anyone that night.

The knife ad been stolen from a vehicle by the 12-year-old and given to his client to put in her "bum bag" that she had been wearing.

He submitted that his client was moving forward as Kingi was advancing and she pushed the knife out in the direction of his chest and it happened to land in his heart.

"She's thinking this guy is going to grab and bash her ... she's moving, he's moving ... she's unfamiliar with the knife, but, sadly, where the knife lands ... but it was not intentional.

"She's just pushing the knife out in the general direction [of the chest]."

A pathologist's report found the level of force behind the blow was "low to medium", a level "reasonable" for someone who feared for their own safety, Mansfield submitted.

Laybourn reminded the jury of how young and mentally immature his client was at the time - 13.

An expert had given evidence about how young people struggled to comprehend the consequences of their actions at that age and he dismissed the Crown's submission that his client knew what she was getting into when she walked back towards Kingi that night.

"The Crown case is that she should have processed the consequences on two levels; that she agreed that there was a plan to rescue [12-year-old] and that it was a joint enterprise she entered into knowing that it could lead to serious violence and somebody else using a knife to commit very serious injury or death."

He also said his client was nowhere near the older accused when the fatal blow was delivered into Kingi's heart, a stance agreed on by the victim's partner, Vicki Reihana, who was standing behind him at the time.