'I hate my last name': Sister of accused Sydney stabber speaks out, apologises to victims

The sister of the alleged Sydney knifeman has spoken about her guilt and pain for the victim.

"I just wanna say sorry to the....she was younger than me you know?" said Mert Ney's sister on Wednesday.

She declined to give her name.

"She could have been going out for drinks or shopping with her mum, having dinner with her boyfriend. And she can't do that now, can she?" she told media outside her home in Sydney.

On Tuesday afternoon, chaos erupted in Sydney's CBD when Mert Ney, 21, rampaged through the city brandishing a large kitchen knife.

It's alleged he stabbed one woman in the back before being restrained by bystanders and arrested.

The woman was taken to hospital in a stable condition.

After the pandemonium had subsided, a 21-year-old woman, believed to be a sex worker, was found dead in her apartment nearby. 

Ney had made an appointment to see her at 1.30pm, and was caught on CCTV leaving her building at 1.50pm.

"All the words I can say isn't ever going to bring her back," said Ney's sister on Wednesday.

"I'm really sorry, she was defenceless and everything you know," the woman continued.

She said she feels "shocked, angry, [and] disgusted," at her brother's actions.

"I hate my last name," she continued.

She told media Ney had descended into insanity, and that she wants him to "suffer."

"I want them to just put him in the worst mental health institution where it's like jail," she said. 

Charges are expected to be laid against Ney on Wednesday at his bedside at Royal Prince Albert Hospital.