Brent Wyndham, the constable who fatally shot Yamatji woman JC in 2019, began giving evidence at the coronial inquest into her death in Geraldton on Thursday.

He became the first police officer in a century to be charged with murder, however was acquitted of both that charge and manslaughter at a Supreme Court trial in 2021.

The court heard in the moments leading to the incident which caused the 29-year-olds death, JC turned towards Sen. Const. Wyndham and took two steps back, before the WA Police officer yelled four commands: "put the knife down, "get on the ground," "you're under arrest, get on the ground," and "put the f..... knife down," before firing the fatal shot.

He said he was scared when JC took the backwards steps and did not respond to commands.

"I felt scared because she was not listening to what I was saying and I've got a gun pointed at her," he said.

"I thought I was going to get stabbed."

Sen. Const. Wyndham said he did not consider the possibility JC may have been retreating and his colleague, Sen. Const. Adrian Barker, who was closest to JC, was always in his field of vision.

Former police officer Adrian Barker, who was closest to JC when she was fatally shot by Sen. Const. Wyndham, testified on Thursday morning at the coronial inquest into her death on September 17, 2019.

Mr Barker expressed feeling "jaded" and "resentful" towards the police organisation during an internal review in November 2021, where he was made to feel responsible for JC's death.

He disputed the internal investigation's findings that he breached policy, stating defiantly, "there is no such breach".

Mr Barker described the interview as more of an exit interview than a managerial one, saying, "I was a bit more expressive than I otherwise would be".

"Resentful perhaps, with some of the things the organisation has done to me," he said.

The court was informed that Mr Barker resigned from the WA Police Force in November 2021 after 16 years, citing a complex reason for his departure which he declined to elaborate on.

During the internal review, Mr Barker reflected on his actions, admitting frankly, "OK, brutal honesty, I feel it did," when asked if his actions or inactions contributed to the shooting.

He explained he felt he needed to approach JC to facilitate communication and distract her, despite not receiving any specific communication or order to do so.

Mr Barker, now working as a long-haul truck driver, expressed regret, stating that if given the chance, he would have suggested to his colleagues to "hang on, let's just see where this goes," especially before Sen. Const. Wyndham discharged his firearm.

He emphasised, "I thought I was doing the right thing".

"Each individual officer had done the right thing," he said.

JC's family, represented by their lawyers, publicly thanked Mr Barker during the proceedings.

Her foster mother, Anne Jones, and sister, Bernadette Clarke, expressed gratitude for Mr Barker's attempts to calm JC down.

Mr Barker acknowledged their appreciation, saying with humility, "it's nice".

"Thanks to them for not holding anything against me I suppose," he said.

Some of Mr Barker's former police colleagues testified that his proximity to JC may not have helped the situation.

Mr Barker described JC as walking away from him at the time of the incident, and he felt compelled to get closer to communicate effectively without raising his voice.

The internal affairs investigation concluded Sen. Const. Wyndham breached police policy by shooting JC, despite him still serving as a police officer in Geraldton.

The inquest, focusing on police actions, policies, training, tactics and the mental health care provided to JC, continues its proceedings on Friday.