A prominent gangland lawyer who was murdered outside his Melbourne restaurant in 2016 was gunned down for being a police informant, according to new details revealed about the case today.

Joe Acquaro was shot dead out front of Gelobar in Lygon St, Brunswick East, in March 2016. He was walking to his car when he was shot at least five times, before his body was later discovered by a garbage collector.

The Herald Sun has reported underworld figures were convinced Acquaro was a police informant and because of this a $250,000 price was put on his head.

Joe Acquaro was shot dead outside his gelato bar in Brunswick north of Melbourne in 2016. (Supplied) (Supplied)

Acquaro (left) with Rocco Arico (orange shirt), one of his underworld figure clients. (Supplied) (Supplied)

It is believed an interstate hitman was sent to murder Acquaro months before he was found dead. Police have spoken to this person but he is not a suspect in the case.

Acquaro made his name as a high profile criminal lawyer for a number of mafia identities, including drug baron Frank Madafferi.

Homicide squad detectives have interviewed a number of high profile gangland members and it is Acquaro's suspected collusion with police that is believed to be behind the fatal attack.

It is believed Acquaro was gunned down for being a police informant. (Supplied) (Supplied)

Police have spoken to Madafferi, former City of Melbourne councillor Michael Teti and the suspected shooter, according to the newspaper.