Mert Ney had been listed as a missing person by his family following a "domestic violence situation", which prompted a police "concern for welfare report", in the days leading up to Tuesday's fatal stabbing rampage in Sydney's CBD.

NSW Police Commissioner Mick Fuller has also confirmed that the 20-year-old had recently "self-admitted himself [to a facility] following a medical issue" prompting subsequent mental health assessments.

Court documents have also confirmed Mr Ney appeared at Blacktown Local Court on June 24 for possessing or using a prohibited weapon - knuckledusters - without a permit.

Commissioner Fuller said Mr Ney's criminal history was "not remarkable". 

"He has some low-level issues around theft, malicious damage. He had some low-level domestic violence issues link back to his family that, again, were not significant or serious injuries, however they were being investigated."

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