Akiir Muo was pushed out of the stolen car Gargasoulas was travelling in on the morning of January 20, 2017 in Melbourne, and taken to a St Kilda police station where she was kept in an interview room for two hours.

She was not spoken to until after Gargasoulas went on his rampage in Bourke St Mall, killing six pedestrians and injuring a further 27.

When police finally took Ms Muo's statement she told them about Gargasoulas' chilling plan.

"He would drive to the city and run people over if police chased him," she said.

At the inquest into the deaths of Gargasoulas' victims, Assistant Commissioner Stephen Fontana said he did not know why Ms Muo was not interviewed sooner.

"I felt she should have been properly interviewed as a victim straight away and I can't explain why that didn't take place," he said.

Mr Fontana authored a near 500-page internal review into the massacre, which was made public by Coroner Jacqui Hawkins on Wednesday.

In it, Mr Fontana found there was "no explanation" about the "lack of police action in relation to Muo's disposition as a victim, witness or offender".

"A high priority should have been given to interviewing Muo much earlier," he wrote.

Mr Fontana will be back in the witness stand at the inquiry on Friday, to be grilled by lawyers for former police sergeant Frank Caridi.

Mr Caridi, who was not interviewed as part of the review, repeatedly requested the elite Critical Incident Response Team contain and arrest Gargasoulas almost nine hours before the massacre.

Australian Associated Press