Defence barrister Steven Whybrow SC claims Detective Inspector Marcus Boorman made the comment during a clandestine coffee meeting, which occurred while the jury in Mr Lehrmann's trial was deliberating.

A lengthy statement prepared by Mr Whybrow was released on Tuesday by an independent inquiry, which is examining the conduct of authorities involved in Mr Lehrmann's aborted criminal case.

Mr Lehrmann, whose trial was scuppered by juror misconduct, has always denied raping Ms Higgins at Parliament House in 2019, when the pair were Liberal Party staffers.

The inquiry is largely concerned with tensions between Director of Public Prosecutions Shane Drumgold SC, who led the case against Mr Lehrmann, and police, who were worried about Ms Higgins' credibility.

The strained relationship between the criminal justice agencies is on display in Mr Whybrow's statement, which describes how he had coffee with Detective Inspector Boorman on October 25, 2022.

Mr Whybrow claims the detective was "agitated" and concerned about the pair being seen together near the office of the Director of Public Prosecutions, so they went "somewhere in Farrell Place" to speak.

"DI Boorman indicated to me that he was quite distressed about this prosecution and considered that Mr Lehrmann was innocent," Mr Whybrow wrote in his statement.

"He made several other comments along these lines and I recall he said words to the effect 'if the jury comes back with a guilty verdict, I'm resigning'."

Mr Whybrow, an experienced lawyer, said this was a first for him.

"I had never before had a conversation with a police officer who had indicated that they were going to resign because they had been ordered to prosecute someone they considered was innocent," he wrote.

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The defence barrister also detailed an earlier meeting with Detective Inspector Boorman, and a text message exchange in which the police officer asked to be informed of any developments with the jury.

"I have no confidence the DPP will let me know," Detective Inspector Boorman allegedly told Mr Whybrow.

Mr Whybrow was highly critical of Mr Drumgold in his statement, writing that he was concerned the prosecutor "did not act as an objective minister for justice".

"This was a matter that, from the outset, was compromised by adverse media publicity," he wrote.

"In my opinion the DPP failed to take adequate steps to either mitigate the adverse publicity or counsel Ms Higgins (or her supporters) to cease making public statements about the matter."

Giving an example, he claimed Mr Drumgold should have sought a temporary stay of Mr Lehrmann's trial when television presenter Lisa Wilkinson made a problematic speech at last year's Logie awards.

Instead, Mr Drumgold unsuccessfully opposed Mr Lehrmann's application for a delay of his trial.

Mr Whybrow also claims Mr Drumgold made derisive and unjustified comments about senior police officers, including Detective Inspector Boorman.

In one instance, he said the prosecutor approached him during a break in the second week of the trial.

They had a short discussion after Mr Lehrmann's lawyers identified Detective Inspector Boorman and Detective Superintendent Scott Moller as witnesses who were required for cross-examination.

"Any opinion by those boofheads about the strength of this case is not admissible," Mr Drumgold allegedly told Mr Whybrow.

Mr Whybrow goes on, in his statement, to detail a remark Mr Drumgold made during the trial.

In this comment, Mr Drumgold said the skill levels of the police officers involved in interviewing Ms Higgins were "not high".

"I did not, and do not, understand the basis of Mr Drumgold SC's comment," Mr Whybrow wrote.

"I regarded the comment as pejorative, unjustified and inappropriate, particularly as it was made in front of the jury."

Mr Whybrow is expected to be the second witness called to give oral evidence at the inquiry, which is currently hearing from Mr Drumgold.