A former New Zealand Police detective turned private investigator who was paid to tail Auckland businesswoman Elizabeth Zhong in the months before her grisly death told a jury today that his client - who he referred to as "the accused" - seemed under immense pressure.

"I've had many conversations with the accused and he said many times that Ms Zhong had ruined his life," Jimmy Jin said of Fang Sun, who is on trial for Zhong's murder.

"Basically, during the day Mr Sun would have to deal with matters here in New Zealand ... court hearings, meeting lawyers, et cetera. But ... late at night he would have to deal with pressure from China, pressure from investors."

Police found Zhong's body in the boot of her Land Rover on the afternoon of November 28, 2020. Authorities believe she had been stabbed over 20 times the night before, when an intruder entered the bedroom of her East Auckland home.

Prosecutors said at the start of the trial last month that Sun was an estranged business partner who had been furious with Zhong, believing that she had lost him and his family more than $24 million in investments. The two were engaged in a heated civil battle over control of their company, Sunbow Ltd.

Auckland businesswoman Elizabeth Zhong, 55, was found dead in the boot of her Land Rover in November 2020. Photo / Supplied

The private investigator told jurors he began discussions with Sun around July 2020 and agreed to begin surveillance.

"The gist of it is that Ms Zhong had defrauded millions of dollars and he's going to court with her, and Ms Zhong may not want to go to court," he said. "I could tell that he was frustrated.

"Some of these Chinese investors were friends who trusted Mr Sun with their money. But now all their money was in jeopardy, causing these Chinese investors to constantly harass Mr Sun."

Because the two were alumni of the same university in China, Jin said they never signed a contract. But Sun transferred Chinese currency, amounting to roughly $15,000 in New Zealand dollars, to an account in China belonging to Jin's brother.

Fang Sun appears at Manukau District Court in February 2021, charged with Elizabeth Zhong's murder. Photo / Alex Burton

"I basically went to the address when I had time," he said. "I would sit nearby the address for some time and watch the house. I would take photos of the address and send them to Mr Sun via WeChat."

He would sit in his Toyota Camry for an hour or two at a time and look into the home's large dining room window.

"My purpose was to ascertain whether or not Ms Zhong was still staying there, and if possible find put who was visiting her or where she had been going to," he explained.

Multiple witnesses have testified during the trial or submitted statements in which they said they either directly heard Sun make threats against Zhong or were told by Zhong about threats.

Among them was a couple who visited Elizabeth Zhong at her Otago winery one month before her stabbing death. Both recalled today that the Auckland businesswoman was under tremendous stress due to financial strains and threats from a business partner.

"She said things weren't working out with her business partners, and one in particular," Henry Wong told jurors. "She said that he had threatened her.

"I don't know the details about the threats, but I know she wasn't able to sleep because of the threats. They were serious."

Henry Wong's wife, Sharon Wong, recalled the same conversation.

"She said that she was threatened by a man and she is very worried," she testified, adding that Zhong mentioned the name of the man who threatened her but she could no longer recall it. "It was a Chinese name, and she did say he was stranded in New Zealand ... because of the pandemic."