Nicola Gobbo helped convict Melbourne's most dangerous criminals. She was also their lawyer.

Despite reports the Australian Federal Police were attempting to stop Sky News’ documentary about a Melbourne barrister-turned-police-informant from airing, the first half went to air on Monday night.

Presented by Peter Stefanovic, Lawyer X: The Untold Story explored how Nicola Gobbo shared information with police about Melbourne’s criminal underbelly, including her high profile gangster clients.

Among Gobbo’s past clients were drug lord Carl Williams, who was murdered in prison, and drug kingpin Tony Mokbel.

Watch the promo for Lawyer X: The Untold Story. Post continues below video.

Lawyer X.

Nicola Gobbo was one of Victoria’s youngest female barristers, tipped as talented enough to become a future Supreme Court judge.

Before the Court of Appeal revealed her identity in March, Gobbo was known only as Lawyer X or Informant 3838.

The Lawyer X scandal has rocked Victoria’s police and justice system and has prompted a royal commission into the state police force’s conduct during the Melbourne gangland war and its dealings with informants, including Gobbo between 1993 and 2005 and after she became a registered informant in 2005.

According to the Supreme Court, she began giving information in 2003 but was registered from 2005-2009.

The Age reported at least 20 prisoners received a letter from the Director of Public Prosecutions, Kerri Judd QC in December. The letter reportedly told prisoners the criminal barrister provided information on them to Victoria Police that may have been subject to privilege which protects confidential communication and documents between a lawyer and client.

The lawyers for one of these prisoners – gangland getaway driver Faruk Orman – has indicated their client intends to apply for bail after Victoria's Attorney-General Jill Hennessy granted him a petition of mercy in June, ordering his case be reheard before the Court of Appeal.

Orman is serving a 20-year jail term for the murder of career criminal Victor Peirce. He was convicted by a jury in 2009 because he drove the gunman to the murder scene.

The ABC reported drug kingpin Mokbel and convicted drug dealers Rob Karam and Zlate Cvetanovski have also applied for leave to appeal their convictions in the wake of the Lawyer X scandal.

The Untold Story.

The first half of the two-part documentary focused on the 2004 murder of police informant Terry Hodson and his wife Christine, who were murdered in their home in Kew in Melbourne's inner east.

Hodson had been due to testify against former Victorian drug squad detective Paul Dale, after he was caught breaking into a drug house in September 2003 and implicated Dale as the mastermind behind the burglary.

Hodson was Gobbo's client and she was in a relationship with Paul Dale.

Dale appeared in the first episode of the documentary. He denied the allegations.

In previous interviews, Gobbo had expressed fear for her safety.

On June 30, 2015, then known as 'Informer 3838', Gobbo wrote a letter to Victoria Police Assistant Commissioner Steve Fontana which was published by the ABC following the lifting of suppression orders on the case in the High Court in December.

She claimed her information led to the arrests and charging of at least 386 people and she feared for her life.

"My treating psychologist has said on occasion that were it not for my children, she does not think I would still be alive; such is the level of my depression, anxiety and PTSD," Gobbo wrote in the letter.

Veteran journalist Derryn Hinch told The Untold Story he was amazed she was still alive.

In a teaser for the show’s second episode, airing on Tuesday night, an associate of Gobbo is heard saying that he told her that on signing a certain document "Nic... I think you sign your death warrant".

Sky News chief executive Paul Whittaker confirmed to The Australian that Victoria Police had contacted Sky two weeks ago to request to view the documentary in advance of this week's broadcast.

Sky News declined the request.

Part two of Lawyer X: The Untold Story airs on Sky News tonight and streams on Foxtel. Part-one is already available for streaming.