An American woman travelled to Auckland four years ago to help a woman take her own life, but police cannot bring her here to face assisted suicide charges.
Audrey Wallis, 49, was found dead in her Auckland flat in August 2007.
She was not terminally ill but believed to be depressed and suffering health problems from an addiction to prescribed medications.
Coroner Katharine Greig, in a report made public on Tuesday, suppressed details of how Mrs Wallis took her life, but said it was deliberately self-inflicted asphyxiation, where she was assisted in the preparation by another person, who was present when she died.
Mrs Wallis died in 2007 but police began to investigate her death in 2008 following a British documentary which claimed an American woman had travelled to New Zealand to assist in a suicide and been paid in cash.
Susan Wilson - also known as Cassandra Mae, who lives in North Carolina - told a follow-up documentary she had visited Mrs Wallis and accepted $US2000 ($NZ2600) to offset her expenses, but denied she had assisted her suicide.
Early last year, Ms Wilson told the FBI, who were interviewing her on behalf of police in New Zealand, she had watched Mrs Wallis make all the preparations to take her own life, but had not touched anything herself.
She sat with Mrs Wallis for two hours and then removed all the evidence to make it look as if she had died of natural causes.
"I did not assist her in any phase of her death - I was only a witness and a friend who did not judge her choice."
However, police established Ms Wilson provided some material for the suicide.
Ms Wilson told police and the coroner she is not willing to return to New Zealand because she will be arrested and prosecuted.
Extradition agreements between the two countries do not cover charges involving assisted suicide.
Police say Ms Wilson will be arrested if she ever tries to enter New Zealand again and have laid charges against her in her absence.