As one female criminal lawyer faces intense scrutiny for turning on her clients during the height of Melbourne's bloody street war, another has broken her silence.

News broke this week that a lawyer-turned-police informer received millions of dollars from police for information that helped put her own clients behind bars.

The lawyer, who cannot be named but goes by the pseudonyms Informer 3838 and Lawyer X, helped end the gangland war that gripped Melbourne during the late 1990s and early 2000s.

But the way she did it will now be the subject of a royal commission that could lead to reduced or overturned sentences for convicted criminals including Tony Mokbel and Rob Karam.

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Informer 3838 tried for years to persuade the Director of Public Prosecutions not to tell her clients she was an informer. She was unsuccessful and letters were sent to those serving time.

This week, the High Court ruled that suppression orders preventing the story being told were to be lifted.

As the informer now grapples with her very public reveal, and police try to protect her, a former colleague says she tried to expose the turncoat lawyer.

Zarah Garde-Wilson, who dated convicted killer Lewis Caine before he was murdered in the gangland war in 2004, says wanted the story about Informer 3838 told years ago.

"This is clearly just the tip of the iceberg," Garde-Wilson told A Current Affair.

"We first found out about this in 2014 as a fact (and it) took us two years to get the information to file proceedings."

In court documents seen by news.com.au, Garde-Wilson says Informer 3838's identity was no closely-guarded secret.

"The identity of Lawyer X is common knowledge," she said in an affidavit. "At least within the legal fraternity. I am aware of Lawyer X's true identity."

She told ACA that what Informer 3838 did "undermines almost a decade of criminal cases".

"These cases all need to be scrutinised one by one," Garde-Wilson said.

"Every single one of them needs to be wound back to find what did actually go on, were they given a fair trial, and what are the consequences and results if they didn't get a fair trial."

Mokbel and Karam are among the high-profile criminals appealing their convictions. Mokbel was jailed for 30 years for his role as a drug kingpin during the gangland war and Karam was jailed for 37 years for importing more than 330,000 ecstasy tablets.

Chief Police Commissioner Graham Ashton defended police on Monday, saying the use of Informer 3838 was a necessary weapon in an escalating war on Melbourne's streets.

"Over the preceding 12 months, numerous people had been murdered, some in very public locations and high-profile criminals were vying for control of drug operations that were inflicting serious harm on the Victorian community," he said. "It was accordingly a desperate and dangerous time."

The gangland war started in Melbourne in 1998 with the murder of gangster Alphonse Gangitano and claimed the lives of hit man Carl Williams and Jason Moran, among others.

The pressure on police and politicians to end the carnage was immense. It will be alleged it was that pressure that led police to team up with their special informer.

But what they did was, according to the High Court, "reprehensible conduct in knowingly encouraging (Informer 3838) to do as she did".

The informer has reportedly refused witness protection despite the perceived threat to her life. She attended a public function as recently as September.

Informer 3838 is believed to have accepted some form of police protection, but High Court documents reveal she distrusts police.