The ACT's top prosecutor blasted the once confidential report on Monday, telling an independent inquiry into the Bruce Lehrmann case it was "extraordinary" and he had never seen anything like it.

Director of Public Prosecutions Shane Drumgold SC gave evidence as the inquiry, which is examining his conduct, along with the actions of police and ACT Victims of Crime Commissioner Heidi Yates, began.

The independent probe, led by former Queensland judge Walter Sofronoff KC, was ordered after tensions between police and prosecutors became public.

At the heart of their divergent views was a report Detective Superintendent Scott Moller prepared for Mr Drumgold in June 2021, before the decision was made to charge Mr Lehrmann over the alleged rape of Ms Higgins.

Mr Lehrmann denies sexually assaulting Ms Higgins at Parliament House in March 2019, when the pair were Liberal Party staffers.

His ACT Supreme Court trial was aborted last October because of juror misconduct, and the charge levelled at him subsequently discontinued.

The so-called "Moller report" was released by the inquiry on Monday, revealing the senior detective's concerns about Ms Higgins' claims.

"Throughout the investigation Ms Higgins has been evasive, uncooperative and manipulative," Detective Superintendent Moller wrote, listing eight examples.

Among them, he noted discrepancies in what Ms Higgins had told investigators about having received medical treatment.

Detective Superintendent Moller also referred to her reluctance to give police her phones for examination.

Once she had provided one device, detectives found a message in which she told partner David Sharaz she was "clearing out my phone ahead of police".

Investigators also identified an exchange in which Ms Higgins and her then-partner, Ben Dillaway, discussed inappropriate behaviour by staffers at Parliament House about a month before she was allegedly raped.

"During this exchange Ms Higgins agreed with her then partner about the need for an impressive political sex scandal," Detective Superintendent Moller wrote.

"She said, 'Exactly! A sex scandal the party can be proud of. Another Barnaby but without the baby ha ha'."

Later in the report, which was sent to Mr Drumgold for advice on whether to charge Mr Lehrmann, Detective Superintendent Moller gave his views.

He described Ms Higgins' credibility as "the cornerstone of the prosecution case". saying investigators had "serious concerns in relation to the strength and reliability of her evidence".

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The detective also expressed fears for Ms Higgins' mental health and how any prosecution might impact on her wellbeing.

Mr Drumgold was asked about the report on Monday as counsel assisting the inquiry, Erin Longbottom KC, questioned why he had not wanted it disclosed to Mr Lehrmann's lawyers when they requested "investigative review documents".

He was scathing in his assessment, calling the report "extraordinary" and "a basic, misguided analysis" of the importance of certain evidence.

"I had never seen comments of this nature appear in a police brief," Mr Drumgold told the inquiry.

The prosecutor also described it as containing opinions that were based on material that would not be considered admissible at Mr Lehrmann's trial.

"There were very pejorative things said that were based on evidence that was mischaracterised," he said.

Ultimately, Mr Drumgold described being of the view this report and other "investigative review documents" were privileged and "not relevant".

However, he acknowledged the Australian Federal Police owned them.

"The AFP were free to ignore, and did ignore, my position, and disclosed the documents," he said.

Mr Drumgold is set to continue giving evidence at the inquiry on Tuesday.