'Grandiose fantasies' consumed killer taekwondo teacher

Kwang Kyung Yoo, 51, had lied about meeting Gina Rinehart, qualifying for the 2000 Olympics, owning a Lamborghini and living in Sydney's wealthy eastern suburbs, Justice Ian Harrison heard on Thursday.

To impress his own wife, he would send emails to himself, pretending to be important people.

"These are a form of fantasy, essentially a grandiose or self-important fantasy that he's richer, has more social status, has more success in life in different domains than he actually does," forensic psychiatrist Andrew Ellis told the NSW Supreme Court.

"They're psychiatrically unusual because they're quite easily refuted.

"But it's an immature way of managing your own self-image."

In reality, at the time of his arrest, Yoo was in debt and behind on rent.

He owed $3000 on a credit card and another $8000 for his North Parramatta martial arts studio, the agreed facts state.

He and his wife had $10,000 across their bank accounts and cards.

According to prosecutors, Yoo began thinking of murder after seeing the father of a taekwondo student become successful and wealthy.

His mind turned to how he could kill the father, his wife and the seven-year-old student to get their money, the court was told.

By February 2024, he acted - strangling the mum and son in his studio before driving the woman's BMW to the family home in Baulkham Hills and fatally stabbing the father.

After his arrest, Yoo could not explain how he was going to get the family's money and later detailed his remorse.

"I was ... good ... two months ago, now I'm a murderer," he said.

"I feel shame, guilt and sorrow."

Though there was no evidence Yoo harboured any hatred for his victims and a specific motive has not been identified, his lawyer Richard Wilson SC acknowledged the murderer "had some envy".

Yoo on Thursday came face to face with the slain family's loved ones, who wore crocheted flowers on their lapels as they filled the public gallery of the courtroom and laid bare their own grief.

Taking frequent glances at the killer, a supporter read an impact statement from the woman's parents in Korean - Yoo's head bowing lower and lower as the words washed over him.

"Our lives have been utterly destroyed," an English translation of the statement said.

"Ordinary days, small happinesses, laughter and conversation - all of them have disappeared.

"What remains is only excruciating pain and endless despair."

Sobs and sniffs reverberated through the courtroom.

Yoo did not raise his head as the parents recounted how their daughter, son-in-law and grandchild were killed.

"Even now we can still hear the screams and tears," the statement said.

"Every moment we breathe is painful and being alive in itself feels like a punishment."

The mother's brother made a lament to the heavens, asking what his family had done to deserve a tragedy like this.

"Why were our ancestors so cruel to us?" his victim impact statement said.

"What wrong did we commit that they had to take her and upset mum?"

Yoo's interpreter began wiping away tears as the brother described everything he wished he had told his younger sister, aged 41.

"Mum's vanity table is piled high with tissues soaked in tears as she thinks of you," his statement said.

"Whenever I was struggling, I knew I could reach out to you - my only little sister.

"Now I am left alone, what do I do?"

Shortly before the murders, Yoo had lied to his wife, telling her a school where he worked would soon provide him with a BMW.

He would arrive at Westmead Hospital in a BMW belonging to the deceased, an hour after the 39-year-old stabbed him in self-defence.

Yoo will be sentenced on December 16.

Australian Associated Press