A Hungarian migrant who was assassinated with his Thai partner at a property near Sunbury in 2003 was a heavy gambler with unexplained wealth.
The state coroner, Judge Jennifer Coate, has found that Steve Gulyas and Tina "Bing" Nhonthachith died from "gunshot injuries to their heads by person or persons unknown".
Homicide detectives believe that Nihal York, a Sri Lankan businessman, holds the key to solving the execution-style killing of the couple.
Gulyas and his partner ran a sham love-for-sale agency on the internet.
The Partner Search Australia agency may have been a front for bringing Asian prostitutes into Australia.
Mr Gulyas also had "associations with a number of high-profile criminals in Australia" and had "unexplained overt signs of wealth" according to police.
Homicide detectives also discovered that he attended "casinos in Australia where it is alleged he had turned over hundreds of thousands of dollars".
Federal and Victorian police were investigating him, as was the tax office.
One of his associates was Nik Radev, the head of the Russian mafia in Australia, who was shot seven times when he stepped from his car in Coburg in April 2003.
The coroner found that "there were suspicions that Steve was involved in illegal immigration schemes involving bringing females into Australia from south-east Asian countries to work as prostitutes and the illegal importation of motor cars".
The coroner also said that detectives had conducted a significant investigation into "two persons of interest, each apparently with motives relating to financial disputes over business dealings . . ."
One of those persons was York and the other is a Thai woman known as "Superporn" who is believed to be involved in the sex trade and the introduction industry.
Veteran homicide Detective Ron Iddles, who is heading up the cold case squad, said police had tracked the Thai woman to New Zealand, while York is believed to be on the run overseas.
"We have spoken to the woman in New Zealand in relation to a conversation she had with the deceased woman (on the day of the deaths)," the detective senior-sergeant said.
"We still need to speak to Nihal York as we believe that he holds the key to solving the crime," he said.
Mr Gulyas, 49, and his partner Ms Nhonthachith, 47, were both shot three times in the head on October 19, 2003.
Police believe that they knew the killer or killers. They died on an isolated property that they owned at Wildwood, as there was no sign of forced entry and theft had not been the motive.
A $200,000 reward is on offer to help solve the double murder.
Anybody with information is urged to contact Crime Stoppers or police.