Yet as part of a broader probe into police brutality in Ballarat and the proficiency of the force's internal reporting system, IBAC is investigating an allegation that a mentally unwell woman, who was arrested for being drunk in a public place, was kicked and stomped on, as she lay handcuffed on the ground inside the Ballarat Police Station. It was alleged the woman was strip-searched in front of male officers. David Grace, QC, argued on behalf of the two officers in the High Court on Tuesday, that IBAC did not have the power to force the officers to self-incriminate. He said the watchdog did not have the ability to override the common law privilege against self-incrimination. This privilege entitles a person to refuse to answer questions if the consequence would be self-incrimination. Solicitor-General for the State of Victoria, Richard Niall, QC, argued that the watchdog had the power to investigate people suspected of, but not charged with a crime.

"The position changes fundamentally, in our submission, on charge," he said. Mr Grace, QC, was probed on this point by the judges, given that the officers had not been charged. He argued that police officers retained the privilege to not self-incriminate when the watchdog had reasonable grounds to suspect that they have behaved illegally. A prosecution would be likely, based on evidence gathered by IBAC, he said. "In this case it is way beyond suspicion," he said. "We say it is belief on the part of the Commissioner and it is certainly stronger in terms by the Counsel Assisting in his opening address."

Mr Niall, QC, argued that given that IBAC's investigation would involve events which had occurred at the Ballarat Police Station, the officers stand in a "marked different position from civilians", as they were compelled to respond to questions about police conduct. "The role of police and the obligation to give an account of what happened is a very important part of the context of construction," he said. Public hearings for the case have been placed on hold until a decision by the High Court is made. This is the first time the core function of IBAC will be tested in the High Court since it was set up in 2012.