Senior police were kept updated about ‘Lawyer X’ Nicola Gobbo’s tip-offs about the crimes of Melbourne’s major underworld figures, officers noted in their diaries at the time.

But their former boss – once Victoria’s top underworld investigator – says those records aren’t necessarily accurate.

Now a royal commission is left wondering who to believe.

Jim O’Brien was head of the gangland-busting Purana Taskforce from 2005 to 2007, when some of Victoria’s most notorious crooks were at their most active.

Some were about to be brought down by the underworld soldiers they’d recruited to do their dirty work.

Police handlers who spoke to turncoat barrister Ms Gobbo sometimes multiple times a day, have recorded updating Mr O’Brien about various tips she passed on.

But Mr O’Brien, who had a reputation among colleagues as a meticulous note taker, has little or no record of some of those conversations.

“I didn’t go out of my way not to record things in my diary which is what you seem to be suggesting,” Mr O’Brien told the commission from the witness box on Monday.

Counsel assisting Megan Tittensor has compared Mr O’Brien’s diary notes with others multiple times throughout his evidence, which as gone for several days.

Mr O’Brien suggested there may have been officers recording that they’d updated him in order to protect themselves.

“Quite often what people do in the police force is try to acquit their process,” he said.

“They might have put it in an incident report. Doesn’t actually mean that I received it.”

Unless the information was in his diary, he didn’t get it, he said.

There have been times Mr O’Brien acknowledged the information passed on to him was of little interest and not worth a diary entry.

On one occasion handlers noted that Ms Gobbo wanted to speak to him about now-convicted drug trafficker Milad Mokbel and a suggestion Mr O’Brien needed to “rattle his cage”.

“I don’t appear to have a note of it,” Mr O’Brien said.

“I would have paid scant regard to that sort of comment.”

-AAP