A woman accused of murdering her partner called police 16 times in the years before his death - each time feeling scared, threatened or fearing for her safety.

And the court has heard from the only witness to the alleged murder, the woman's teenage son.

Karen Anne Ruddelle is on trial in the High Court at Auckland for the murder of Joseph Michael Ngapera in November 2018.

The court was told that after returning home from a local bar the pair argued in Ruddelle's Manurewa home.

Ruddelle's 14-year-old son woke and jumped in between the pair to protect his mother.

She then picked up a 19cm knife and stabbed Ngapera twice, piercing his heart.

He died soon after despite efforts by Ruddelle's son to save his life.

Ruddelle does not dispute that she killed the 56-year-old - but denies it was murder.

She says her actions were in self defence - that she was terrified of Ngapera because of years of domestic violence and that he initially lunged at the knife.

The Crown called evidence from about 40 witnesses before the defence opened its case today.

• 'I've just murdered someone I love': Woman on trial for murder

The only witness to the alleged murder, Ruddelle's youngest son - who cannot be named - was not called.

But the statement he gave police soon after Ngapera was stabbed was read to the jury.

'I heard mum scream'

He said he woke up to his mother's screams for help and got up immediately.

"I think she stabbed him with a knife, I think she's drunk - she doesn't usually drink," the boy said.

"The knife had a black handle…. Looked like a filleting knife.

"I can't remember exactly but I think mum stabbed him on the left shoulder."

He said his mother then threw the knife but he did not see where it went.

"I think my mum got upset because Joseph was talking about my sibling in a negative way," the boy told the officer.

"I wasn't away when they were fighting I just woke up from my bed when I heard mum scream

"I walked into the kitchen, I pushed Joe away because he was arguing with mum...The next thing I knew mum had a knife and stabbed Joe."

Police tried a number of times to meet with the boy and interview him more formally and at length.

However, his family would not give permission.

Love, violence - and 111 calls

Earlier this week the jury heard that Ruddelle and Ngapera had a rocky relationship punctuated by violence.

They were known to police, who had been called a number of times to incidents involving the pair.

Details of those calls - 16 between July 2015 and October 2018 - were read to the jury today.

They heard that Ruddelle would often call police in the early hours of the morning when Ngapera was intoxicated.

Sometimes she too had been drinking - but it was mostly her partner affected by alcohol.

Numerous times she told police that Ngapera had threatened to "murder" her.

On various occasions he told her he'd been convicted of murder in Australia, that he was responsible for a number of "unreported" violent assaults in South Auckland and that he was carrying a knife in his bag.

Police attended Ruddelle's home each time she called 111 but she usually declined to make a statement or give any further information.

In the first call she told them she could not answer further questions as if Ngapera found out she was speaking to the cops he would kill her.

She would tell police, or call them back and say she did not need them, that she was "fine" and had sorted things with Ngapera.

Other times she told officers she had "made up the threats".

Ruddelle told police repeatedly that she was "frightened" of Ngapera and he was threatening and intimidated.

She said she felt vulnerable when she was home alone.

In 2016 the couple broke up but Ngapera would still arrive at Ruddelle's home in the night, usually drunk.

One time he entered her bedroom and woke her to accuse her of saying another man's name in her sleep.

He became angry and questioned her about whether she was seeing someone new, she told police.

She said Ngapera slapped her, but would not make a formal statement.

In June 2016 Ruddelle obtained a trespass order against Ngapera.

But that did not keep him away.

She called police again the next month when he turned up at 4am and became "verbally aggressive".

"She was scared and wanted him gone," Crown prosecutor Chris Howard told the jury.

She asked police for help to get a Protection Order and told them there were "historic
assaults" that she had not reported.

She said she did not want to report them.

In July 2016 Ruddelle was granted a protection order that also covered her youngest son.

But contact with Ngapera continued.

She continued to call police but was reluctant to speak to officers, questioning whether
she would have to make a statement every time he breached the order

In March 2017 Ngapera was convicted of a breach and things seemed to settle until
November when Ruddelle again called 111 when her partner showed up at her home.

She refused to make a statement when police arrived.

In September 2018 Ruddelle had the order discharged.

Her last call to police was on October 4, 2018 when Ngapera arrived home intoxicated.

She called for help "before things escalated".

A month later she allegedly murdered her abuser.

Earlier today the jury heard from forensic pathologist Rexson Tse who conducted the post-mortem examination on Ngapera.

He explained that the first stab wound was fatal, passing through Ngapera's muscle, ribs, lungs and heart.

The second was 9cm deep.

He said it was possible that Ngapera had lunged at the knife, but that would have only caused one wound.

The second would have had to be caused by someone pulling the knife out and "reinserting" it in his chest.

The trial, before Justice Matthew Palmer, continues.