Victoria Police had "unhealthy" relationships with informers during Melbourne's gangland wars, a former drug squad boss says.
While reviewing how police dealt with sources in the early 2000s, then-drug squad boss Tony Biggin said the recruitment was the wrong way around.
"There was a feeling that Victoria Police ... had probably been recruited by informers rather than recruiting informers," Mr Biggin told Victoria's royal commission into the management of police informers on Wednesday.
"So we were actually doing it the wrong way ... providing information back or in fact entering into unhealthy relationships with informers."
His comments came amid a grilling about his knowledge of turncoat lawyer Nicola Gobbo as she informed on her own clients.
Mr Biggin said he had only been told around October 2005 that Ms Gobbo, now infamously known as Lawyer X, was registered as a source.
"I recall thinking that this was unusual," the former officer said in a statement to the commission, released as he gave evidence.
"I was aware that Ms Gobbo was a barrister."
Mr Biggin told the commission he assumed at the time Ms Gobbo's dual roles as a barrister and an informer were being managed by her handlers.
He said he only realised the nature of the information Ms Gobbo provided to police after being asked to review her interactions with handlers in 2006.
The officer thought using Ms Gobbo as an informant was a high-risk strategy but decided it was worthwhile.
"In the benefit of hindsight, I accept that the risks associated with Ms Gobbo's profession as a barrister were not at the front of my mind," Mr Biggin said in a statement to the commission.
"Were they in your mind at all?" Counsel assisting Andrew Woods asked the former officer.
"They were in my mind but not ... ringing bells," Mr Biggin replied.
At the time, he said he didn't necessarily know who Ms Gobbo's clients were and, even then, thought she only dealt with their bail applications.
But months later he had changed his mind about using her as a source and thought the force should end it.
But the force continued to use Ms Gobbo as an informer.
She gave information to police on-and-off between 1995 and 2009, and continued to do so unofficially until 2010.
The royal commission continues.