Former Victoria Police chief commissioner Simon Overland has told a royal commission he did not know Nicola Gobbo was informing on clients she was acting for, in breach of her legal obligations to them, as his investigators never told him.

Key points: Simon Overland was an assistant commissioner when Ms Gobbo was registered as an informer in 2005 and has since left the force

Simon Overland was an assistant commissioner when Ms Gobbo was registered as an informer in 2005 and has since left the force He said he could not recall whether or not he raised the risk of using Ms Gobbo with then-chief commissioner Christine Nixon

He said he could not recall whether or not he raised the risk of using Ms Gobbo with then-chief commissioner Christine Nixon It is Mr Overland's first day of evidence at the Royal Commission into the Management of Police Informants

On the stand for his first day of questioning at the Lawyer X royal commission, Mr Overland said he was not part of a 2005 plan to sign up Nicola Gobbo as a human source.

He said he was surprised and concerned when he discovered shortly afterwards that she had been registered as an informer.

Mr Overland — the assistant commissioner in 2005 — set up the gangland Purana Taskforce and is credited with bringing an end to Melbourne's gangland war.

Lower ranks of police, including Purana detectives, have previously told the commission their use of Ms Gobbo was sanctioned by police command, and evidence suggested it went all the way to Mr Overland as the then-assistant commissioner of crime.

By the time Ms Gobbo was signed up for her third, and most prolific, stint as a police informer in 2005, she had been acting for Tony Mokbel for three years.

Ms Gobbo would be used extensively by police to bring down Mokbel's drug cartel.

"At no time was I made aware that she was breaching legal obligations — if I had been I would have taken action," Mr Overland said.

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'Mr Mokbel was never going to let her go'

Mr Overland insisted Ms Gobbo came to them, not the other way around.

He said she was in fear for her life as Mokbel was never going to let her walk away from being the syndicate's lawyer.

While accepting Ms Gobbo's work as a police agent was a risky, Mr Overland said the alternative was worse.

He saw it as a lose-lose situation.

"Mr Mokbel was never going to let her go," he said.

He agreed it was a dangerous position for her to be a police informer, but thought she would ultimately be killed anyway.

"I thought the alternative course of action was more risky than this," he said.

He said she had put herself in a position where "her life was under serious threat" because she had crossed boundaries" and as Mokbel's lawyer, was facilitating his drug network. "

"I did consider whether that was an appropriate thing to do. But I thought the alternative of leaving her out where she was was worst, because I thought in all likelihood she'd get killed." Mr Overland said.

Barrister Nicola Gobbo was used as a police informer between 1995 and 2009. ( ABC News: Greg Nelson )

In 2009, when he was deputy commissioner, Mr Overland pushed for Ms Gobbo to be made a witness over the murder of Terence Hodson and his wife Christine.

The inquiry previously heard her police handlers disagreed with the move and drew up a briefing note outlining concerns that Ms Gobbo's exposure as a human source would risk convictions and damage Victoria Police's reputation.

Mr Overland told the inquiry he did not recall seeing the briefing note.

From 2009, he sat on a steering committee overseeing Taskforce Petra, which investigated the Hodson murders, and Taskforce Briars, which investigated a separate 2003 gangland murder.

Counsel assisting, Chris Winneke, asked him if he had ever raised organisational risks with his boss, then-chief commissioner Christine Nixon.

"Is it your belief that you did not inform chief commissioner Nixon about the use of Ms Gobbo as a human source?" Mr Winneke said.

"I don't have a recollection either way," Mr Overland said.

Mr Overland said he never took notes or made diary entries about Ms Gobbo, which was a common practice by police command who worried her use would become known.

Both Chief Commissioner Graham Ashton and Assistant Commissioner Luke Cornelius told the inquiry they did not take notes regarding Ms Gobbo.

By 2006, three killers — all represented by Ms Gobbo — rolled and implicated each other and Carl Williams in a number of gangland murders.

Asked how that was allowed to happen given Ms Gobbo's legal obligations, Mr Overland said it was done with the full knowledge of the Director of Public Prosecutions (DPP).

But he quickly admitted the DPP was never told Ms Gobbo was a police informer.