Mr Hadley directly contacted NSW police commissioner Karen Webb, at the request of her father millionaire John Singleton, to ask if 25-year-old Dawn had died in the attack.

The radio host revealed he had the difficult task of calling Mr Singleton to confirm his nightmare.

She was one of six people killed in the attack by Joel Cauchi on shoppers at the Sydney mall. A further 12 people were injured including a nine-month-old baby.

"I rang him and he said, 'I think my Dawnie is one of those who lost their life and I can't confirm it,'" Mr Hadley told 3AW radio.

"Can you do something?" Mr Singleton reportedly asked Mr Hadley.

The radio host said he called NSW police commissioner Karen Webb to confirm the victims' identities.

"I rang the police commissioner and asked her if she had any names and she said only one and confirmed it was Dawn," he said.

"And I had the job of ringing John back and unofficially confirming that his dear darling daughter had been stabbed to death by this lunatic."

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The 25-year-old Ms Singleton was one of three daughters to Mr Singleton and lawyer Julie Martin.

She was reportedly at the Westfield shopping mall's Chanel store to buy makeup ahead of her upcoming wedding to childhood sweetheart Ashley Wildey.

Mr Wildey, an officer with NSW Police, was among those who rushed to the shopping centre at 3.30pm when the first calls to emergency services were made.

He discovered that his fiance was one of the victims when he arrived on the scene. Mr Wildey was escorted away from the shoppng centre to be comforted by family.

Outpourings of grief over the 25-year-old's death have come from her friends, former colleagues and her alma mater, Kambala School.

The school paid tribute to their former student in a message to parents saying she was a valued member of their community.

Kambala School principal Jane Danvers said "we extend our sincere condolences to her family and acknowledge that the loss of a family member from such a random act must be exceptionally hard to comprehend".

"There is no doubt the ramifications from this incident may continue to unfold over the coming days and weeks with many of our community potentially affected," she said.

Ms Singleton worked in e-commerce for fashion company White Fox. She was mourned by her employers in a post to social media.

"Over the weekend we lost not only an employee of White Fox but someone special to us who felt like a family member," the tribute read.

"We are all truly devastated by this loss.

"Dawn was a sweet, kind hearted person who had her whole life ahead of her.

"She was really amazing."