The young man allegedly behind a deadly stabbing rampage in Sydney’s CBD spent just 20 minutes in an apartment building for a meeting with a woman believed to be a sex worker who was later found dead.

The 24-year-old woman was killed – believed to have had her throat slit – and a 41-year-old woman was stabbed in the shoulder yesterday, allegedly by Mert Ney who was seen running around the city’s streets with a butcher’s knife about 2pm before he was detained by heroic bystanders.

“Initial inquiries indicate the man had attended the unit for an appointment about 1.30pm and was captured on CCTV leaving the building about 1.50pm,” NSW Police said in a statement today.

The woman’s body wasn’t found until 3pm, in the midst of the extensive police operation.

Commissioner Mick Fuller said footage has been obtained of Ney in the city, “predominantly” CCTV from the City of Sydney council, in addition to the 20-year-old’s phone and past records.

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Officers have established Ney made phone contact ahead of an appointment with the 24-year-old victim, who was found dead in an apartment on Clarence St with her throat slit.

“We’re rebuilding his movements,” Commissioner Fuller told reporters today.

He said potentially the past two years of Ney’s life will come under the microscope to aid what will be a long-term investigation.

When asked about Ney’s whereabouts in the past week, the commissioner said the 20-year-old’s family had listed him as a missing person due to concerns for his welfare.

“Police had taken a report for that, and a report around a domestic violence situation,” he said.

“He was on the system as ‘keep a look out for him’ for both of those things … so from our perspective, again, that is not unusual in terms of what we see day in and day out in some houses across NSW.

“And that is not a common theme for someone to then take the next step of coming into the streets of Sydney with a knife and killing people and threatening to kill people.”

Commissioner Fuller said it appears Ney recently self-admitted to hospital “following a medical issue” and there were subsequent mental health assessments.

Ney reportedly presented to the Blacktown Hospital emergency department on August 7 due to a drug overdose and was later discharged, according toThe Daily Telegraph, but then absconded from an ambulance on August 8 while in the care of paramedics.

Ney is also believed to have been living in places other than his family’s home in Marayong, in Sydney’s west, in the days preceding his dramatic arrest.

“There’s a property in Blacktown where we believe he was staying, so we’re looking at that premises,” Commissioner Fuller said, noting it was subject to a search warrant overnight.

“If he’s been couch-surfing and homeless for some time, then we need to find every location that he’s stayed in.

“We need to backtrack his history, not just the last 48 hours, but the last, potentially, two years.”

Nine News reported Ney was “agitated” and “rambling” the night before the stabbings, telling other youths in a “safe house” that he’d been kicked out of home and had left a mental hospital.

The police commissioner said they are looking for additional crime scenes.

“I ask if anyone saw something suspicious, if there’s a neighbour or a person who saw changes in him (Ney), or saw him go to any place of worship, please come forward,” he said.

“Any piece of information will be so important in terms of piecing this together quickly and making the necessary links, if we need to, to terrorism or to other potential crimes.”

Commissioner Fuller said Ney had some “low-level issues” around theft and malicious damage, and some domestic violence issues linked back to his family, but described his criminal history as unremarkable.

Ney remains under police guard at Royal Prince Alfred Hospital and is yet to be charged.