Acquaro was known to police but not as a convicted person, police say.
The father-of-three had strong ties within the Calabrian community and had been president of Melbourne's Italian Chamber of Commerce and the Reggio Calabria Club.
He was also a criminal lawyer who had represented a raft of prominent gangland figures in Victoria.
Court documents show there was a A$200,000 contract on his head, and he had been warned by police his life was in danger.
The Herald Sun reports this bounty was increased to A$500,000 in recent months.
Acquaro was aware of the threat against him but was not worried, the newspaper reported today.
"I'm isolated. They can't physically harm me," he told the newspaper recently.
"I'm not afraid of dying." The lawyer had taken over the popular gelateria and cafe on Lygon Street about five years ago.
Gelobar was damaged in a suspicious fire in January.
- AAP