The family of a young woman who was murdered by her housemate in Sydney say she had believed there were "no bad people" in Australia but really she was "surrounded by a demon".

In a three-page letter given to news.com.au today, the parents of Qi "Kathy" Yu said their family had "collapsed" since their daughter was killed by her housemate, Shuo Dong, in Campsie on June 8, 2018.

They said she had been an intelligent, beautiful, lovely and innocent girl – "the apple of her parents' eye from an early age".

Dong, 20, pleaded guilty in the NSW Supreme Court today to murdering 28-year-old Yu.

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Yu came to Sydney in 2009 and completed her studies at the University of New South Wales, receiving a Bachelor of Electrical Engineering and a Masters in Telecommunication.

"Her experience from years of Australian life was that Australia was good for everything," her father, Zhihe Yu, said in the letter.

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"Good for air, good for food, good for environment and good for others.

"However, there were unexpected storms in the sky. Qi Yu was surrounded by a demon person.

"Our daughter was murdered in cold blood. Nearly 10 years of hard work suddenly ended in vain and a bright future was ruined."

He said his daughter's life had been "destroyed by this devil".

Forty-seven days after her disappearance, Yu's body was found wrapped up and dumped on the side of the M1 motorway near Mount Kuring-Gai in the city's northwest.

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Phone signals had narrowed the search to nearby bushland which police scoured for weeks.

Nearly 200 people in a WeChat group organised by her classmates, colleagues and friends also joined the search every Saturday and Sunday in the "suspicious area", the family letter states.

The young woman's parents had issued an impassioned plea for information on June 26, 2018.

"Both of us cannot sleep every night … my wife's tears run dry," Yu told reporters at the time as his wife, Qing He, sobbed next to him.

She held up a poster reading, "Looking for missing girl Qi Yu" and was photographed in tears.

u was last seen in Campsie, in Sydney's southwest, in the unit she shared with Dong and another woman.

"Qi Yu and her housemates had been getting along well," her father said in the letter.

"Her only drawback was that she had no sense of defence against other people.

He said Yu and her mother spoke via WeChat "almost every day for hours, talking about life, shopping, work … everything".

u had been on the phone to her mother in China via WeChat about 7.15pm on Friday, June 8, 2018, when she hung up abruptly.

Dong had spent that evening bickering with Yu over cutting his lease short and bond money he owed her, according to documents previously presented to the local court.

Her parents heard the argument in the background when the power to Yu's unit shut off.

They later contacted a neighbour who lived nearby to check on their daughter.

Facts tendered in December state at about 10.30pm, Dong opened Google Maps while on the M1 at Mount Colah to search for directions back home, The Sydney Morning Herald reported.

Yu's Toyota Corolla was found abandoned on a street in Burwood, about 4km from her home, the next day. Blood-like stains were found through the vehicle and the home.

Before the killing, Dong also searched "what are the penalties for murder in Australia" online.

Yu's other housemate, a young woman, raised the alarm with police on Saturday morning.

Dong will face a sentence hearing for the murder before Acting Justice Peter Hidden on May 18.

Justice Elizabeth Fullerton today said: "It may well be His Honour can sentence that week."

Dong's lawyer said they were waiting for jail records to be sent to a psychiatrist so an updated report could be given to the judge, and they were yet to go through the amended statement of facts with Dong before they were signed.

Yu's parents want her killer to be "punished at the highest level" and jailed for life.

The maximum penalty for murder in NSW is imprisonment for the term of one's natural life.

"Our family has suffered a serious disaster and our family was destroyed," Yu said in the letter.

"Unable to accept the loss of my daughter, my wife grieves inconsolably, wakes up from heart pain almost every night and is on the verge of an emotional collapse.

"She wanted to depart from this world herself and join our daughter."

Yu resigned from his job in Shanghai to come to Australia with his wife because she was "physically and mentally impaired" by the loss and "could not handle all kinds of affairs" on her own.

"We have not only lost our only daughter, but also lost our support, hope and motivation to live," he said.

"He killed not only our daughter Qi Yu, but also Qi Yu's parents."

Yu told news.com.au today they had to move away from Campsie because in "every corner" was the memory of Yu.

"Every day in this process is a bad moment," he said.