Revealed: Michelle Leng's terrifying last hours before her uncle brutally murdered her

WARNING: Disturbing content

In the hours before her uncle murdered her, Michelle Leng lay alive naked, bound, gagged and terrified on her bed as he filmed her with his phone.

The images of Ms Leng show black duct tape and a white cloth around her mouth, and an expression of "fear and terror" on her face.

It was Friday, April 22, 2016 and although she was running out of time before she would be brutally stabbed to death, it was days before her body would be found.

Michelle Leng, left, at her aunt's 2012 wedding to Derek Barrett, right, who murdered his niece four years later.

At some point while she was still alive but restrained in her bedroom inside her aunt's Campsie unit in western Sydney, Ms Leng's cousin arrived home downstairs.

The young woman was unaware that her cousin was bound and captive in a room above her, at the mercy of Ms Leng's uncle, Derek Barrett.

Just two years younger than the portly IT worker who was married to her aunt, Ms Leng was facing the final hours of what was meant to be a better life pursued in Australia.

Instead she would be murdered because of Barrett's sick obsession for the pretty young university graduate.

Michelle Leng left China to pursue her dream of studying in Australia but was brutally murdered by her obsessive uncle, Derek Barrett.

Her body was thrown into the same NSW Central Coast waterhole she had photographed as a tourist three years earlier.

Ms Leng's body would be found floating face down in the Snapper Point blowhole and the perverted things that were done to her can now be revealed after her killer has pleaded guilty.

AAP reported on Thursday that Derek Barrett, 28, has pleaded guilty to the murder and filming Ms Leng while she was alive.

Appearing via video in Burwood Local Court, Barrett admitted indecently assaulting his niece before murdering her and dumping the body in the blowhole in April last year.

Barrett also pleaded guilty to taking or detaining a person with the intent to obtain advantage and three counts of committing an act of indecency with a person aged over 16 years.

The identikit that NSW police issued after Leng's body was discovered at Snapper Point.

It can now be revealed that Barrett filmed his victim showering in the Campsie home they shared with her aunt and him masturbating over her as she slept.

Images found on Barrett's phone show Ms Leng, naked, bound and gagged on her bed.

The 25-year-old from Chengdu, who was also known by her Chinese name of Mengmei, had left China in 2011 to study.

Ms Leng's mother, who doted on her daughter following the death of her husband in an earthquake, believed Ms Leng would be safe living with her aunt.

In 2016, Ms Leng's aunt, 48, often spent time in Wollongong for work; the woman's daughter, Ms Leng's cousin, also lived in the Campsie flat.

Videos ranging in length from 30 seconds to two minutes show Barrett masturbating over Ms Leng as she slept.

Police say Barrett recorded himself setting up a camera in the bathroom used by Ms Leng, hidden behind toiletries.

In videos retrieved from Barrett's phone, Ms Leng can be seen coming into the bathroom, undressing and showering.

The blowhole at Snapper Point on the NSW central coast where Leng's body was found by tourists. Photo / news.com.au

In one video, Barrett appeared to be "preparing a bath" before calling out to Ms Leng, who was later filmed in the bath.

On the day of her death, Ms Leng was bound and gagged by Barrett in her bedroom, and photographed by him restrained and scared.

Her aunt was away for two days in Wollongong.

Barrett then murdered Ms Leng, stabbing her more than 30 times.

Two days later, on Sunday April 24 last year, Barrett drove Ms Leng's naked body to Snapper Point and disposed of it in the water.

Tourists found the body the same day, but because it was unidentified police released a computer generated image of the dead woman's face.

When Ms Leng's aunt arrived home from Wollongong, she made Barrett accompany her to report her niece as a missing person to police.

Ms Leng was positively identified as the Snapper Point body three days later; back in China, family and friends were devastated by the news.

Mei Zhang, Michelle Leng's mother, weeps at a Sydney press conference. Photo / news.com.au

Officers studied CCTV footage of Ms Leng shopping at Pitt Street in Sydney's CBD on the Thursday before she disappeared, and catching a train from the city to Campsie train station.

The following day, on April 30, police charged Derek Barrett with Ms Leng's murder.

Ms Leng's mother, Mei Zhang, flew from China to Sydney and spoke of her terrible loss at a press conference.

Ms Zhang bowed her head and wept as she described her close relationship with her daughter and the pain of losing her.

"We even today still cannot accept the fact that she has left us and we are still in great suffering," Ms Zhang said.

"The time will never turn back to when Mengmei and I were living happily together."

Last year, Derek Barrett's lawyer told news.com.au that his client was having a "very unpleasant" time in custody at Silverwater Correctional Centre.

Barrett will face a hearing in the NSW Supreme Court in October.