Martin Joseph Matthew Marinovich has denied the charge of murder despite admitting to police he killed his mum.

An "isolated" man who admitted killing his mother was not "overly emotional" when he was charged with his mother's murder, a court has heard.

Martin Joseph Matthew Marinovich​ is on trial at the High Court at Auckland. He accepts his mother, 59-year-old Nolene Ann Marinovich​, died at his hands on February 7, 2019, but denies murder.

The 28-year-old was arrested the day afterward at their house on Carter Rd in West Auckland's Oratia.

The Crown claims Marinovich "snapped" and killed his mother by striking her with a hammer in the head at least 12 times after the pair argued.

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The court has previously heard how Nolene had multiple health problems and Marinovich was her main carer.

CATRIN OWEN/STUFF The red-handled hammer Martin Marinovich admitted using to strike his mum in the head 12 times with.

On Tuesday, Detective Lee Bigelow told the court Marinovich was "calm" when he formally arrested him for the murder of his mother.

"I don't know what to say, it's all like a bad dream," Marinovich told Bigelow at the Henderson police station about 4.30am on February 8.

Marinovich told the detective the pair had had an argument but he "couldn't even tell you what it was about".

"I remember having my hands around her neck, then it's a blur. I must have grabbed the blanket and then the hammer from the bookshelf. I couldn't tell you how many times I hit her. I remember once," Marinovich told Bigelow.

Under cross examination, defence counsel Shane Tait asked Bigelow how Marinovich appeared when he was formally charged.

"He was calm, reflective...I think he was considering what had taken place and how it would affect his life," Bigelow told the court.

"He was not overly emotional. I don't think he was surprised [with being charged]."

Detective Lorella Harrison also spoke with the defendant in the early hours of February 8.

She told the court he appeared "anxious" and "nervous".

Marinovich also told Harrison he didn't know "how to feel" and he "couldn't even cry".

"I asked him what was worrying him and he said, there was toilet that was broken at his home, and they didn't have enough money to repair it ," Harrison said.

The court previously heard how the broken toilet had been a point of tension for the mother and son.

"I CAN'T COPE"

Earlier on Tuesday, Janet Daniel, Nolene's friend of 40 years, said she visited her in hospital on February 4, just days before her death.

She observed Marinovich in a "very agitated" state, "twitching" and "spaced out", which was abnormal, Daniel said.

As Daniel left the hospital, she asked Marinovich if he was OK. He said: "I can't cope, I can't cope anymore", she said.

Nolene and Daniel would speak on the phone everyday and Daniel would occasionally visit the Carter Rd home.

Just before Christmas of 2018, Daniel visited the house. She said it "was very grubby".

LAINE MOGER/STUFF Nolene Marinovich was found bludgeoned to death in her house on Carter Rd in Oratia.

"He's been looking after her [Nolene] since he was 9 years old and the last few years have been very hard for him as she became incontinent," Daniel said.

Under cross examination, Daniel told defence counsel Shane Tait the Marinoviches used to keep the house spotless and it was Nolene's "pride and joy".

Earlier on Tuesday, the court heard from Detective Anna Fager, who said the Marinovich house was "very cluttered" with mould in the kitchen.

"It was a very dirty house and most surfaces and items had a thick layer of dust," Fager said.

The court previously heard how the cleanliness of the house had been a cause of concern for Marinovich, especially the broken toilet.

The detective said Marinovich's room was also "very messy" with dirty clothes all piled up.

RYAN ANDERSON/STUFF Crown Prosecutor Robin McCoubrey.

A number of cards and communications between Marinovich and his mother were found by police, including a postcard saying "I love you Mum" in Marinovich's bedroom.

The trial is set down for two weeks and will continue on Wednesday.