Melbourne drug kingpin Rocco Arico is hoping conversations between slain lawyer and police informer Joseph Acquaro and detectives could be the key to his release.
Arico was jailed in 2017 for 14 years, with a minimum of 10 years, for extortion, intentionally causing injury, possessing a firearm and drug trafficking.
His jail term was later cut by two years, with a minimum period of nine years.
On Monday, Victoria Police commissioner Shane Patton was ordered to provide documentation, including record of interview, diary notes and transcripts of conversations, between his officers and Mr Acquaro to Arico's lawyers.
Mr Acquaro was never officially registered as a police informant, but it has previously been revealed he provided information to police about another client, crime boss Frank Madafferi.
Arico argues that by secretly giving information to Victoria Police about clients, Mr Acquaro, who acted for him between 2006 to 2016, robbed him of his right to a fair trial.
Mr Acquaro was shot dead outside his East Brunswick gelato shop in March 2016.
Chief Commissioner Shane Patton described the request as "no more than a fishing expedition", highlighting that the only informing done by Mr Acquaro had already been identified in another case.
Supreme Court Judge Jonathon Beach found Arico had a "legitimate forensic purpose" for seeking the documents and ruled that the chief commissioner must provide the documentation.
Madafferi is currently fighting convictions he believes were tainted by Mr Acquaro's snitching.
Victoria Police's use of informants has come under a cloud since the Lawyer X scandal, involving gangland lawyer Nicola Gobbo.
Since then, numerous high-profile criminals have come forward to appeal their sentences - most notably Tony Mokbel.
Mokbel has already had one conviction overturned and is appealing another.
