No one was ever arrested over Emanuel Sapountzakis' death. An inquest ruled that he was probably the victim of a robbery that turned violent.

But after making their first major breakthrough in the baffling case, cold-case detectives now suspect a group of known criminals were responsible.

Mr Sapountzakis had been recently married and had a two-year-old daughter when he was killed.

His family has pleaded with anyone who knows what happened to him to come forward.

"Emanuel did not deserve this; no one deserves to be murdered this way and be found the way he was found," his sister Mary Sapountzakis said.

"Please come forward and you will bring at least some answers,  and bring justice for him."

The 25-year-old moved to Australia as a child but was planning to return to Brazil to be closer to his parents, and took up driving taxis to save extra money.

He picked up his final fare in a Ford taxi on Boronia Road, Boronia, just after 2am on March 2, 1993.

Witnesses have told police they saw Mr Sapountzakis drive south on Stud Road with a man in the front passenger seat and turn into the Police Paddocks Reserve in Dandenong.

It was there a woman discovered Mr Sapountzakis' body while walking her dog about 8am that same morning. He had been shot in the back of the head and had bruising on his arms that suggested a struggle.

His abandoned cab was found shortly after on Mountain Highway in Bayswater, out of petrol and with $86 on the still-running meter.

Police were unable to identify any suspects at the time, nor could an inquest in 1997, which ruled that the young man was likely the victim of a robbery that had turned violent.

But a recent tip-off to police led to several new witnesses being interviewed, say police.

Detective Senior Sergeant Boris Buick, manager of Victoria Police's cold case investigations, said suspects had been identified who were all known to police and were involved in the drug trade.

He said it appeared Mr Sapountzakis could have been involved in their criminal activities or owed them money.

"In the context of that relationship, or that group of people that he was involved with, something has occurred and he's been killed because of that," Senior Sergeant Buick said.

Detective Senior Sergeant Buick said new information suggested a Maroon Nissan Skyline sedan, with the partial registration DSD, was involved.

Ms Sapountzakis said although nothing could bring her brother back, solving the case would bring answers to a family still haunted by the killing.

"Every time there's a milestone in our family – when a new child is born, the anniversary of his death, or his birthday – it's as if it's just happened again," Ms Sapountzakis said.

"Anyone who does have information is probably in turmoil, they are probably suffering the same way as we are. Come forward, and that turmoil will end."

Police have urged anyone with information to call Crime Stoppers on 1800 333 000 or make a report at www.crimestoppersvic.com.au.

patrick.hatch@fairfaxmedia.com.au