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A West Auckland man who killed his mother after years of caring for her has been found guilty of murder.

Martin Marinovich killed his mother Noeleen Ann Marinovich in their Oratia home on February 7 last year but denied it was murder.

The Crown alleged he tried to strangle his mother and then bludgeoned her to death with a hammer, striking her head multiple times.

However, the defence claimed the victim was fatally strangled and later struck with the hammer in a case of manslaughter.

He could not remember how many times he hit her in the head with a hammer.

Justice Tracey Walker summarised the case for the jury this morning, saying that the defendant admitted he killed his mother in an unlawful act and that was why he was guilty of at least manslaughter.

It was up to the jury's to decide if it was manslaughter or murder.

"You must decide the case without being influenced by sympathy, emotion or prejudice one way or another," she cautioned the jury.

A charge of murder, particularly in these circumstances, could give rise to strong feelings, she said, but feelings of sympathy must be set aside.

The jury must decide the facts based on the evidence presented in court alone, she said.

They returned their decision after three hours.

During his trial, Martin Marinovich recalled fighting with his mother over money on the night she died.

"She wanted to go to Queenstown for her birthday, we didn't have enough money. We didn't even have enough money to fix the toilet," he said.

They faced each other in the lounge and shouted at each other.

"I'm not sure how long we were there for - at some point during that argument, I can only describe it like a light switch turning on."

He got so angry that it was not even anger, it was more like rage, he said.

"I continued to strangle her, essentially for what felt to me like 10, 15 minutes at that point."

He pulled a blanket off the sofa and placed it on her neck.

He noticed "blood poured out of her nose" and at that point he believed his mother was dead, he claimed.

He could not remember how many times he hit her in the head with the hammer.

Earlier the 28-year-old told the court about life with his mother, who he had always known suffered from bipolar.

"Particularly when I was younger she would have quite bad manic phases."

She threw things around the house, he said, and had delusions people were coming to get her.

"As a young child you naturally believe what your mother says to you."

He cared for his mum throughout her worsening health as she suffered from incontinence and in the past couple of years it had taken a toll on his sleeping pattern.

"I became incredibly exhausted … it just got away from me … the cleanliness of the house."

Money was "extremely tight" as they relied on his mother's benefit, which was about $549 a week.

But the pair had always maintained an "extremely loving" and close relationship, he said.

As her only child, there was "no question" he would look after her when she became ill.

However, when she was hospitalised about a week before her death he confided in a family friend that he could no longer cope. He told the court this was a "cry for help".

Marinovich will be sentenced in April.