The chilling last words and final psychotic moments of Whangarei gunman Quinn Patterson's life have been revealed to the Weekend Herald.

In a cold and calm manner Patterson told his best friend and former partner, "I've shot [them] ... they're dead on the front lawn".

Christina White, 66, has spoken exclusively to the Weekend Herald from her Queensland home in Gympie about the man she knew for 27 years.

It is the first time she's talked about Patterson, who is at the centre of Operation Weather, the police investigation into how he came to shoot dead property manager Wendy Campbell, her daughter Natanya and wound contractor Jeff Pipe on July 26.

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She may have also been the last person to ever speak with Patterson before his Mount Tiger Rd home went up in flames following a firefight with police.

Patterson phoned her just moments after killing the Campbells when they entered the Northland property for what was supposed to be a routine property inspection.

When he rang just after 10.50am, Patterson said: "They're dead on the front lawn. I told them, they wouldn't leave me alone, they kept harassing me - I told them I'd shoot them. I have."

White said she'd never heard him so calm.

"He said, 'you're my last phone call, I'm ringing you to tell you I love you and I'm saying goodbye'."

Patterson told White he wouldn't survive the day, but never mentioned he would take his own life or burn his home down.

His final words to her were: "I can hear the sirens, the police are coming, I've got to go."

The Weekend Herald posed a series of questions to police about White and Patterson's relationship, but police said while the investigation continues they were unable to answer specific questions which may be relevant to ongoing inquiries.

However, White said she was interviewed by Queensland Police for about two hours on Thursday on behalf of their New Zealand counterparts.

Patterson, 55, was a man who learned to be a criminal during a stint in prison for stabbing a police officer, White said, and who, in his final years and months, descended into a psychotic siege-like state of mind.

She first met Patterson in Australia in 1990, before the couple moved to New Zealand in 1993, living in several places around Whangarei - including briefly at another house on Mount Tiger Rd.

As White grew to know him more she learned about his "crazy upbringing".

"[His family] believed in aliens and it was, you know, doomsday preppers ... There was always the little grey men who were going to come and sort everything out. Quinn believed in all this, he was brought up with it," she said.

White said Patterson also had alcohol and drug addictions but was "worse" when he was not using.

She left him in about 2010, moving back to Australia to be with her family as Patterson's "psychotic episodes" increased. But the pair stayed in near daily contact with each other.

"He enjoyed his cars, we use to play cards and games, we bush walked, we travelled, we went down to the South Island and travelled around there for a bit, but then he started to get really psycho and I thought 'this is the time for me to leave'," White said.

Read more: Quinn Patterson's friend and love reveals the mad mind of a killer

Patterson moved into his final home on Mount Tiger Rd, but soon began having issues with his tenancy, White said.

Patterson sought help from doctors and psychiatrists during his life, but in the last year his doomsday mentality increased and he began to build his cache of weapons, she said.

"He rang me and said, 'you've got to put some food aside, you've got to store water and get organised because the world's going to end'."

He also built a shooting platform in his backyard for target practice. Police visited him over the structure but decided it was a tenancy issue, despite Patterson not holding a firearms licence.

The Herald earlier revealed that Patterson was using TradeMe to sell accessories for military weapons right up to the day of his death.

And this week, 61-year-old Michael John Hayes was charged with supplying military-style semi-automatic weapons to Patterson.

"I knew he had guns. When he started buying guns I thought, 'this is not going to end well'," White said.

However, she didn't contact police, believing Patterson wouldn't carry out his many threats against the property managers who visited him.

She said Patterson was worried about eviction, but refused to leave until his lease was up.

"They were pushing him and pushing him, he rang me and he said, 'I warned them, I told them to leave me alone or I'd kill them'," White said.

In one email, obtained by the Weekend Herald, Patterson wrote to White: "It's a strange feeling knowing I'm the sanest person (or so it seems)."

She said on July 26 that Patterson simply went "berserk", after being pushed to the brink and having nowhere to go.

Patterson's badly burned remains were recovered from the charred wreck of his rented home. It is still unclear exactly how he died.