A knife-wielding alleged killer who terrorised Sydney’s CBD before being tackled by a man with a chair appeared to have researched massacres before his violent rampage.

Mert Ney, who lived with his mother in Marayong, in Sydney’s west, is expected to be charged with murder as well as serious assault.

The family home has been turned into a crime scene as police hunt for further clues and attempt to piece together what might have triggered the random attack.

A USB stick that contained information on the Christchurch massacre and similar mass deaths in the US was found on the blood-stained accused man when he was arrested by police on Tuesday afternoon.

NSW Police Commissioner Mick Fuller said while the rampage appeared to be the work of a “lone actor”, Mr Ney did, however, have “some ideologies in relation to terrorism” and the Joint Counter Terrorism Team would examine if the terrorism threat needed to be reassessed.

“There was certainly information found on him about other crimes of mass casualties and mass deaths around the world,” Mr Fuller said.

Mr Fuller confirmed Mr Ney had a “long history of mental illness” leading up to Tuesday’s bloody city rampage.

Former classmates have described him as “weird” and someone who needed help.

The troubled 21-year-old allegedly used a butchers’ knife to stab one 41-year-old woman in the back at the Hotel CBD and tried to stab countless others as he wandered the streets.

He is believed responsible for the earlier murder of a young woman – reportedly a sex worker found with her throat slit – whose body was later discovered at a Clarence Street apartment.

A 41-year-old woman was stabbed in the back outside Hotel CBD. Photo: AAP

Mr Ney’s violent rage through Sydney’s CBD instilled terror at the end of the lunch rush hour as he shouted “Allahu Akbar”, and demanded “shoot me, f–king shoot me in the f–king head” and jumped on a Mercedes bonnet.

He was eventually stopped by a random assortment of bystanders who chased him through the streets and brought him to the ground with a cafe chair and milk crate.

A dishevelled and bloody Mert Ney after his arrest on Tuesday.

Commissioner Fuller hailed the workers who ended the “terrifying carnage” as “highest-order heroes”.

They included IT staff, traffic controllers and firefighters who were determined to prevent any more casualties as they chased him through the CBD. They eventually caught Mr Ney near Wynyard Station, pinning him to the ground with a cafe chair and slapping a milk crate over his head.

Westpac IT manager Simon Fuller, who ran after Mr Ney along York Street, eventually got close enough to tackle him with the chair.

“All I wanted to do was stop him and put him on the ground,” he told The Daily Telegraph.

“I followed him up York Street and tried to get him to look into my eyes rather than anyone else around him.”

Other inner-city workers who got involved were advertising account director Michael Appleby, IT manager Simon Finch and recruitment business owner Paul O’Shaughnessy, with his brother Luke and some mates.

Paul O’Shaughnessy was among those who stopped the attack. Photo: AAP

Commissioner Fuller said Mr Ney was known to police but had an “unremarkable history”.

“Ney’s long history of mental health problems appeared to be behind the attacks,” Commissioner Fuller said.

A former classmate from Blacktown Boys’ High School told The New Daily Mr Ney usually “kept to himself” at school and did no harm to others.

A photo of Mert Ney in Year 8.

“[He] was just really weird, like not many mates,” the man said.

“I even went to primary school with him my whole life, [he] was just always the odd kid.”

Mr Ney spent Tuesday night under police guard in hospital.

Commissioner Fuller was asked about reports Mr Ney might have absconded from a mental health facility before “breaking” on Tuesday.

“The evidence all points to that,” he said.

The woman who was stabbed in the back is in a stable condition in hospital.

Mery Ney is pinned to the ground and arrested. Photo: AAP

-with AAP