On the same night authorities believe an intruder broke into businesswoman Elizabeth Zhong's East Auckland home and stabbed her over 20 times in her bedroom - nearly decapitating her - a private investigator had sent a short message to the man who would later be charged with her murder.

"Always there," Jimmy Jin told Zhong's estranged business partner, Fang Sun, via WeChat.

The message, Jin explained to jurors today at Sun's trial, referred to a tracking device illegally placed underneath Zhong's Land Rover that showed the vehicle had remained stationary at her home for the past 22 hours.

The next day, Zhong, 55, would be found wrapped in a blanket in the boot of the Land Rover.

Fang Sun is on trial at the High Court in Auckland, charged with the murder of Elizabeth Zhong on November 27, 2020.

Prosecutors say Sun had a stewing rage directed at Zhong after believing she had lost his family over $24 million in investments in their shared business, Sunbow Ltd, and its subsidiaries. The two were engaged in an ongoing civil battle over control of the company.

Zhong was found dead on November 28, 2020, and Jin, a 19-year veteran of the police department who had gone into private investigating work, had been paid to follow her for four months prior.

While Jin had spent hours parked on the street outside Zhong's house in the past, he told the court today he wasn't there on the night of her death. He instead relied on the tracking device to update his client on Zhong's whereabouts, he said.

The next morning, after waking up early to play tennis with his wife, he received a call from the defendant.

"He said something significant happened," Jin recalled, explaining that Sun said his wife had been "walking in the neighbourhood and saw lots of police" at Zhong's address.

"He advised me not to go over there," Jin testified.

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

But the private investigator told jurors he had another priority - making sure his former colleagues still on the force didn't find out about the tracking device.

"At that time I was still thinking the police presence was caused by one of Ms Zhong's tactics to avoid going to the court [for the civil case]," Jin said. "I was guessing that Ms Zhong was trying to hide away or something.

"So I looked at the app and looked at the location of the vehicle and found out it was not far from Ms Zhong's house."

When Jin arrived at the Sunnyhills neighbourhood where both Zhong and his client lived, Jin said he saw a marked police car parked behind Zhong's Land Rover and a crime scene vehicle arriving on the scene.

He walked past the vehicle and stayed at a nearby primary school while police appeared to dust for fingerprints on the vehicle.

"When I returned, walked back...the marked patrol car and other vehicles were gone," he said. "Ms Zhong's Land Rover was still parked on the roadside. There was no one around, so I just walked to the driver's side of the vehicle, knelt down and removed the tracking device."

Prosecutor Gareth Kayes showed jurors a CCTV screenshot of the private detective in the neighbourhood at 3.40 that afternoon, which Jin acknowledged was himself. As he quickly left the neighbourhood, Jin took a video of the area to show his client but decided against it.

"The whole matter just all of the sudden escalated with the police involvement," Jin said, explaining that he tried calling Sun multiple times a short time later but got no answer. "I became more nervous and didn't want to send the video to anyone."

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

Jin said he also got nervous about the tracking devices.

"I knew the police would be asking questions," he explained. "I was hoping that the homicide inquiry would blow over pretty soon so the police would not find out that I had put a tracking device on Zhong's vehicle.

"So I made the decision to abandon the tracking devices and their boxes. I believe I eventually just chucked them in my rubbish bin."

Jin said he did eventually get in contact with Sun later that evening, and the two met for two hours at a McDonald's restaurant near his house at around 1am the following morning.

By then, the media had already reported widely that Zhong's body had been discovered. But Jin said he still believed she was missing at that point and discussed with the defendant where she might have gone.

However, he acknowledged, he was "feeling quite strange" about the entire matter because it was strange for police to be taking a missing adult so seriously who was gone for less than 24 hours.

"It was too soon," he said.

Jin's testimony is set to continue this afternoon in the High Court at Auckland.