Junior officers in Victoria police warned that using barrister Nicola Gobbo as a police informer risked jeopardising future prosecutions more than a decade ago.

But senior ranks, including future chief commissioner Simon Overland, paid no attention to the suspicions about using the informant known as Lawyer X, a royal commission was told on Thursday.

Assistant commissioner Neil Paterson admitted to the inquiry in Melbourne that some officers warned that using Gobbo – a criminal barrister – as a registered informer risked undoing police work.

“These are issues being raised by relatively junior members of the police force in late 2008, being raised to police at the very highest echelons of Victoria police including (Mr Overland),” counsel assisting the commission, Chris Winneke QC, said.

“That’s correct,” Paterson replied.

Despite the concerns of junior officers, Paterson said legal advice was not sought until October 2011.

Gobbo was first registered as a police source in 1995, again in 1999, subsequently between 2005 and 2009, and continued providing information unofficially until August 2010.

Paterson told the commission he was “very surprised” the reported concerns had not been followed up.

He earlier told the commission that Overland and his predecessor as chief commissioner, Christine Nixon, should and would have known Ms Gobbo was being registered as an informer in 2005 to inform on her clients during the gangland war.

“This is absolutely an assumption I make. Absolutely, my expectation would be that they were fully informed and making themselves aware of all the matters, providing guidance and assistance,” he said on Thursday.

Paterson said it was a period of “significant violence” with people being shot and killed in public and in close proximity to others not involved in the “criminal milieu”.

“I’m quite sure the chief commissioner of that time would’ve been paying particular attention to what had been occurring,” he said.

He also supported Winneke’s proposition that the point of registering Gobbo in 2005 was to “bring about the downfall of various members of the Mokbel family”.

Drug lord Tony Mokbel was among Ms Gobbo’s clients.

“Yes … broadly (in relation to) the Mokbels, and all of the organised crime and a number of murders that were committed at that time,” Paterson said.

A report by anti-corruption watchdog Murray Kellam in 2015 found there had been major failings by Victoria police around their use of Gobbo as a source, amounting to “negligence of a high order”.

“It was left to Gobbo to self-regulate her legal and ethical responsibilities,” corruption watchdog representative Murray Kellam said in a 2015 report.

This analysis was revealed in Paterson’s statement to the commission.

The Independent Broad-based Anti-corruption Commission was notified about Gobbo in March 2018, and of another six possible problematic sources in December.

Gobbo and murdered lawyer Joe Acquaro are among eight members of Melbourne’s legal sector reported to have had dealings with police as possible informers.

A number of witnesses are due to give evidence to the commission on Thursday, including Sergeant Trevor Ashton who was the first person to register Ms Gobbo as a “very good” source, and Assistant Commissioner Jack Blayney who labelled her a “loose cannon” in 1996.

That was 18 months after he was involved in a drug bust on her Carlton property that led to the then Melbourne University law student receiving a bond without conviction for possession and use of cannabis and amphetamines.