Police warned Melbourne man off Acquaro

Police visited alleged mafia kingpin Tony Madafferi last year and warned him they knew where to look if gangland lawyer Joe "Pino" Acquaro was ever gunned down.

Mr Acquaro, who was killed in an apparent execution-style hit on Tuesday outside his Brunswick East cafe, may have been a source for a journalist who wrote about Mr Madafferi.

Court documents that form part of a defamation case brought by Mr Madafferi against The Age newspaper reveal police visited him in mid-2015 to warn him off taking any action against Mr Acquaro.

Detectives told him they had information there was a $200,000 contract on Mr Acquaro's life and if something happened to the lawyer they would "know where to start looking".

"I am instructed by Mr Madafferi, and I believe, that he was and remains extremely upset and distressed about the visit," lawyer Paolo Tatti said in a statement in September.

"He denies the suggestion that he would ever engage in such conduct."

There's no suggestion Mr Madafferi was involved in this week's murder of Mr Acquaro.

Mr Madafferi, who owns several supermarkets and a share in the La Porchetta restaurant chain, is suing The Age over articles that suggested he was the head of the mafia in Melbourne and linked to murder, extortion and drug trafficking.

Melbourne journalist Nick McKenzie has never confirmed Mr Acquaro was one of his sources but in a sworn statement Mr Madafferi's lawyer says he believes Mr Acquaro and the journalist met several times.

The court documents were suppressed until Thursday when a judge lifted the order.

Mr Madafferi's legal team unsuccessfully argued that linking the "incredible coincidence" of Mr Acquaro's death with their client in the media would unfairly suggest he was responsible.

Georgina Schoff QC this week said it "beggars belief" that someone would be stupid enough to murder a person after being spoken to by police.

Mr Acquaro had strong ties within the Calabrian community and had been president of Melbourne's Italian Chamber of Commerce and the Reggio Calabria Club.

As a criminal lawyer he'd represented a raft of prominent gangland figures in Victoria, most recently Rocco Arico, who is accused of extortion.

Mr Acquaro had also worked for Mr Madafferi and his brother Frank, a convicted drug dealer.

He was close friends with Frank but the pair had a falling out in 2013.

Homicide detectives are now working with the Purana task force - which handles organised crime in Victoria - on the murder investigation.

"We want to make sure intelligence is brought in from other jurisdictions (to) make sure we're not missing anything," chief commissioner Graham Ashton told reporters on Thursday.

"We have a lot of hardened, organised crime expertise in Purana."

Police want to speak to anyone who heard shots or a car travelling fast on St Phillip Street where Mr Acquaro's body was found by a rubbish truck driver around 3am.