Ex-police chief Christine Nixon kept in the dark about Nicola Gobbo

Victoria's former police chief Christine Nixon says she was never told about barrister-turned-informer Nicola Gobbo until it became public last year.

Ms Nixon is the latest in a string of retired senior police to be quizzed at the royal commission investigating Ms Gobbo's scandalous role as Informer 3838.

Christine Nixon, shadowed by her deputy Simon Overland, in a press conference about police corruption in 2007.Credit: Mario Borg

She was chief police commissioner from 2001 until 2009 at the height of Ms Gobbo's informing.

Ms Nixon told the royal commission on Wednesday that she only found out about Ms Gobbo's role as a police informer in December last year after a High Court judgment led to her identity becoming public.

Ms Nixon said she should have known and should have been told by her deputy, Simon Overland.

“Do you think that’s something you ought to have been told?” commission lawyer Megan Tittensor asked.

“Of course,” Ms Nixon replied.

“Who do you hold responsible for that?” Ms Tittensor said.

“I assume people like Simon Overland would have been one, he’s the person who has continuity through this process, perhaps there were others,” Ms Nixon said.

Her evidence puts further pressure on Mr Overland, who was her trusted deputy at the time and knew about Ms Gobbo's role. He succeeded Ms Nixon as chief commissioner.

Nicola Gobbo was registered as police Informer 3838 from 2005 to 2009, while Christine Nixon was chief commissioner.Credit: ABC

Mr Overland, sacked as Whittlesea Council chief executive last week, told the inquiry this week he could not recall telling Ms Nixon.

Media reports about the mysterious "Lawyer X" began in 2014, before Ms Gobbo's identity was revealed in December last year. Ms Nixon said she thought "Lawyer X" was another female lawyer, not Ms Gobbo.

Like Mr Overland and other senior officers in force command at the time, Ms Nixon did not keep a police diary so the inquiry is unable to verify her evidence.

"I don't have any documentation," Ms Nixon said.

"I understand Victoria Police has looked. I don't recall it - being told she was a human source and correct, there isn't a record that I can find."

Ms Nixon said she kept out of operational matters after being burnt by the Milte affair.

Kerry Milte, a former barrister, private investigator and Commonwealth policeman met Ms Nixon in 2002 after she was told he had information about corrupt Victorian police.

An Office of Police Integrity report later found Ms Nixon had been duped into appointing the influential "Mr Fix-it" to provide information to a taskforce, dubbed Operation Clarendon, to investigate Italian organised crime in Victoria and interstate.

The report said Mr Milte instead used the taskforce to promote his career and himself as a well-connected police insider and Ms Nixon allowed him to hand-pick three officers to work with.

He chose police with whom he was friendly and for whom he had acted as an informer, including former drug squad detective senior sergeant Wayne Strawhorn, who was convicted of serious drug trafficking charges and jailed for seven years in late 2006.

Mr Milte also nominated former police commander Rodney Lambert, who had responsibility for the disbanded drug squad but resigned from the force under a cloud in 2005.

The actions of drug squad detectives such as Strawhorn led to Ms Nixon disbanding the squad and overhauling the way the force managed informers.

On Wednesday, Ms Nixon said the Milte incident was a serious embarrassment for her and led to her taking a step back from investigations.

"I needed to ensure I was distant and removed from those operational matters, both for my benefit and also for the organisation's," she said.

The Lawyer X scandal this year led to jailed getaway driver Faruk Orman walking free after his murder conviction was overturned because of Ms Gobbo's involvement in his case.

Ms Nixon's evidence to the commission comes after Mr Overland claimed not to know who Ms Gobbo was defending at the time.

But he admitted the saga was potentially illegal and could have perverted the course of justice.

"Certainly I agree the ethics were f---ed," Mr Overland said while being questioned on Tuesday.

He is due back in the witness box after Ms Nixon finishes giving evidence.

Her evidence continues.