Lee-Anne Cartier does not mince her words when it comes to Helen Milner.

Milner became known as the Black Widow after murdering her husband - Cartier's older brother Philip Nisbet - and staging his death as a suicide.

"I just hope she dies in there," Cartier says of Milner's life imprisonment.

"I don't think my nephews should ever have to deal with walking past her on the street," she said of Nisbet's sons to previous relationships.

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Milner laced her second husband's dinner with poison in May 2009 and made his death look like a suicide. But Cartier thought it was suspicious and started looking into the circumstances around her brother's death which eventually led to Milner being charged with murder.

Lee-Anne Cartier giving evidence in the trial of Helen Milner for the murder of Cartier's brother Philip Nisbet. Photo / File.
Lee-Anne Cartier giving evidence in the trial of Helen Milner for the murder of Cartier's brother Philip Nisbet. Photo / File.

Now the story of Cartier's fight for justice will be told on screen in Catching the Black Widow set to show on TVNZ1 tonight. Cartier herself plays a court registrar in the TV movie while her central role is played by Outrageous Fortune actress Aidee Walker.

Eight years after her brother's murder, Cartier wants to confront Milner but the Black Widow blames Cartier for her demise and would not accept a visit from her last year at Arohata Women's Prison near Wellington.

"I've never had it out with her. At what point does your brain come up with this thing and actually think it is justified?"

Milner, now 53, covered up the murder of the Christchurch truck driver, presenting Cartier with a suicide note just weeks after Nisbet's death.

But she didn't count on Cartier noticing the signature was fake.

The realisation that Milner had likely killed her brother sparked Cartier's two-and-a-half year amateur investigation which culminated in Milner's trial in December 2013 where she was found guilty of murder and attempted murder.

Philip Nisbet and his sisterLee-Anne Cartier. Nisbet was murderd by Helen Milner.
Philip Nisbet and his sisterLee-Anne Cartier. Nisbet was murderd by Helen Milner.

The court heard that Milner was motivated by a $250,000 life insurance policy and avoiding a costly divorce, and had made at least one earlier attempt on Nisbet's life.

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Cartier told the Herald on Sunday her investigation, which she pursued because police believed the death was a suicide and did not take her concerns seriously at first, took a huge toll on her personally and financially.

Then living in Caloundra on the Sunshine Coast of Australia, the book-keeper spent tens of thousands of dollars on flights to and from New Zealand, on phone calls, and on tracking down witnesses in a bid to gather evidence.

"Plus it was the lost income. Every time I went back to New Zealand, because I was casual I wasn't earning money. I maxed out Mum and Dad's credit cards."

Milner's web of lies would come crashing down as Cartier disproved each deception including that her brother had narcolepsy, that Milner had taken a DNA sample from Nisbet's body as he lay in the funeral home, that Nisbet was a male escort, and that Ben, Nisbet's then 14-year-old son with his former wife Karen Porter, was not his biological son.

Milner insisted Nisbet killed himself over that.

"I paid for a DNA test to prove that Ben was Phil's son, to prove that was a lie," Cartier said.

Lee-Anne Cartier (left) with Aidee Walker. Walker is playing Cartier in the TV film Catching the Black Widow and Cartier is palying the court registrar.
Lee-Anne Cartier (left) with Aidee Walker. Walker is playing Cartier in the TV film Catching the Black Widow and Cartier is palying the court registrar.

The case also took her away from her own children including twin daughters who were only 9 at the time.

"There would be the mornings before work where I'm ringing the police and where I'm hand-signalling the girls to hurry up and get ready and not really being a mum.

"I look back now and now they're 17 I'm really isolated from them a bit. There are still times where they're angry at me about it."

As the months ticked by Cartier kept up her investigation, all the while not letting on to Milner about her suspicions until she couldn't keep it in any longer and sent an explosive text message accusing Milner of killing Nisbet.

Milner forwarded the message to police who warned Cartier over her communication.

"She thinks she's so much more intelligent than anyone," Cartier said. "She thought she was playing me and I was her little gopher."

Cartier continued to gather evidence until police finally investigated her claims and eventually charged Milner with murder.

Cartier said she's never really recovered financially, although a payout from police to compensate her for their initial botched investigation and the work she put into getting the case in front of a coroner, had at least paid off her parents' credit cards.

She was disappointed that detectives in the first investigation never apologised to her family but grateful to Detective Inspector Greg Murton for reopening the case.

Following her fight for justice, and inspired by people she met along the way, Cartier is now studying for a Bachelor of Criminology and Justice at the University of the Sunshine Coast.

She hopes to work in the criminal justice system to make the process less stressful for victims.

Cartier also wrote a book about the case, published last year by Penguin, and helped producers with Catching The Black Widow.

Catching The Black Widow screens tonight, 8.30pm on TVNZ1 as part of the Sunday Theatre season.

Key dates in the case against Helen Milner

April, 2009:

Makes two attempts in one day on Philip Nisbet's life, hospitalising him both times.

May, 2009: Milner crushes antihistamine drug Phenergan into Nisbet's dinner. The 47-year-old was allergic to the drug and either died in his sleep or was suffocated by Milner.

June, 2009: Milner shows sister-in-law Lee-Anne Cartier a typed suicide note from Nisbet with a fake signature which prompts Cartier to begin gathering evidence against Milner to give to police.

November, 2010: The coroner holds an inquest into Nisbet's death.

May, 2011: The coroner rules no proof of suicide and police reopen the case.

October, 2011: Police arrest Milner and charge her with murder and two counts of attempted murder.

August, 2012: Milner is jailed for 2 years 8 months for perverting the course of justice for earlier framing her own son, Adam Kearns, for a crime that never happened.

December, 2013: After a 13-day trial, Milner is found guilty of murder and attempted murder by a jury in the High Court at Christchurch.

February, 2014: Milner is sentenced to life in prison, with a minimum non-parole period of 17 years.

August, 2014: The Court of Appeal rejects an appeal against Milner's convictions.

April, 2015: An application to appeal her convictions with the Supreme Court is denied.