The bones of butcher Paul Norton and model Mark Johnson, who were both suspected of being involved in the drug trade, were found at Kurnell in the city's south in October of 2007 and formally identified in 2019.
The area was long rumoured to be a dumping ground for bodies following underworld killings carried out during the 1970s and '80s.
Paul Norton was last seen on April 9, 1989, after spending the day with his sons at Leichhardt Oval watching a rugby league match between the Balmain Tigers and Parramatta Eels.
The 31-year-old was reported missing by his girlfriend on April 14.
Mark Johnston disappeared after meeting friends at the Bellevue Hotel in Paddington on September 1, 1986.
State Coroner Teresa O'Sullivan earlier this year concluded the 36-year-old had been murdered by Smith, who died in Long Bay jail in 2021.
The 76-year-old was serving two life sentences for the murders of brothel owner Harvey Jones in 1983 and tow-truck driver Ronnie Flavell in 1987.
Detective Superintendent Danny Doherty on Monday said both deaths were closely linked to underworld criminals from the 1980s and the main person of interest was Smith.
While Smith was in custody at the time Mr Norton went missing, police believe he was involved in orchestrating the crime.
"We believe that he's still very capable of running things from his jail cell and that his associates and those involved in the drug trade were responsible for Mr Norton's disappearance and subsequent murder," Det Supt Doherty said.
The site where the men's remains were found was "a known burial ground for the criminal world including Neddy Smith and his associates", he added.
While police do not believe the two victims knew each other or were otherwise linked, investigators were looking into possible connections as their remains were found close together.
Mr Norton's car, a blue 1981 Commodore sedan, was found weeks later at a Hertz car rental facility at Sydney Airport's domestic terminal on May 2.
A 1996 inquest determined it was most likely Mr Norton's death was a result of homicide, motivated by his involvement in the drug trade.
Investigators used DNA technology including familial samples to identify the remains.Â
Detectives are appealing for anyone with information about Mr Norton or his death to contact police.
His sister, Margaret Brown, said she hoped the appeal could provide some answers about what happened to her brother, who was one of six children in the family.
"With only four of us remaining, we (would) love to find some answers about what happened," she said.
"Even though it's going back many years, we're asking anyone who might have information to contact police."
Mr Norton was described as being of Caucasian appearance with a freckled complexion, about 165cm tall, of thin build with brown hair.
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