Police and prosecutors had a relationship “beset by tension” from the outset of an investigation into former Liberal staffer Brittany Higgins’ rape allegations, an independent inquiry has been told.

The inquiry was established by the ACT government to examine how police, prosecutors and a victim support service handled the allegations made by Ms Higgins against her former colleague Bruce Lehrmann.

Mr Lehrmann faced an ACT Supreme Court trial in October, but it was derailed due to juror misconduct.

The charges against him were later dropped because of concerns about the impact a second trial would have on Ms Higgins’ mental health.

Mr Lehrmann denies the allegation he raped Ms Higgins in Parliament House in 2019.

Counsel assisting the inquiry Erin Longbottom outlined the evidence expected to be heard during upcoming public hearings.

She said there would be evidence the engagement between ACT Police and the director of public prosecutions (DPP) was “beset by tension from the outset”. 

Points of conflict between the two offices arose from whether it was appropriate for police to interview Ms Higgins for a second time and “confusion” about whether Mr Lehrmann should be charged.

Ms Longbottom said the offices disagreed on how matters affecting Ms Higgins’ credibility should be treated by the DPP and police.

“The apparent close engagement between investigating officers and the lawyers for Mr Lehrmann during the trial led to some distrust between police and the DPP,” Ms Longbottom said.

“Information and statements from witnesses have also raised issues about the DPP’s conduct of the case, both before as well as during the trial.”

The inquiry has collected more than 140,000 relevant documents since it was established in December.

ACT DPP Shane Drumgold, Mr Lehrmann’s defence lawyer Steven Whybrow, Victims of Crime Commissioner Heidi Yates and police officers will be called to give evidence during the inquiry.

Network Ten journalist Lisa Wilkinson is also expected to be called to give evidence.

Ms Longbottom emphasised the inquiry was not about the allegations made by Ms Higgins but rather about how each of the criminal justice agencies conducted themselves during the investigation and prosecution of those allegations.

“Public confidence in the criminal justice system is essential to the maintenance of democracy,” she said.

“A collaborative working relationship between those charged with the duty to investigate crime and those charged with the duty to prosecute crime is essential to any well-functioning criminal justice system.”

Public hearings are expected to start on May 1 and will run for up to four weeks.

Inquiry head Walter Sofronoff will provide a report on his findings to ACT Chief Minister Andrew Barr by the end of June. 

By Maeve Bannister in Canberra