Just one day after the completion of the investigation into the fatal shooting of Australian woman Justine Damond, the Minneapolis police union boss has spoken out in defence of the officer who shot her.

Key points: Lt Bob Kroll defends officer, in response to comments by Attorney Mike Freeman

Lt Bob Kroll defends officer, in response to comments by Attorney Mike Freeman Mr Freeman said Justine Damond's shooting "shouldn't have happened"

Mr Freeman said Justine Damond's shooting "shouldn't have happened" Lt Kroll questions Mr Freeman's objectivity, says Officer Noor should not be charged with murder

Ms Damond was shot by junior officer Mohamed Noor minutes after calling 911 on July 15 to report a sexual assault she feared was happening in an alleyway behind her house.

Minneapolis police officer Mohamed Noor is yet to speak to authorities about what happened that night. ( Star Tribune: City of Minneapolis )

In a letter published in the Minneapolis Star Tribune, Lieutenant Bob Kroll questioned the "lack of professionalism" and objectivity of the top prosecutor, Attorney Mike Freeman, who is considering a murder charge against Mr Noor.

Lieutenant Kroll's letter was published in response to comments made by Mr Freeman at a recent Minneapolis town hall meeting.

At the meeting, Mr Freeman was pressed by local residents as to why Mr Noor was not sitting in a jail "as a civilian would be" after a deadly shooting.

Mr Freeman told the group he could not say much regarding the case but that the shooting should not have occurred.

"I'm saddened by the death of this fine young woman," Mr Freeman said.

"It didn't have to happen. It shouldn't have happened."

Lieutenant Kroll said Mr Freeman's comments at the meeting demonstrated, "he is focusing on the status of the person lost rather than the events leading to a tragic loss".

"This comment breaks with the imperative that fairness cross all socio-economic boundaries," Lieutenant Kroll said.

"Police officers already had reason to worry about their safety. Now they must wonder if they'll be treated with fairness by prosecutors.

"We want an assurance that Noor will not be charged simply on the basis of Damond's status as a fine young woman in a nice neighbourhood.

"The status of the deceased as a fine young woman, while true, is not and should not be part of an objective decision to charge anyone with a crime."

Union boss' history of controversial comments

It is not the first occasion Lieutenant Kroll has raised concerns over the treatment of officers and spoken in defence of those who have used deadly force.

"Everybody now seems to know how to do our job better than us," he told the Star Tribune in 2015, following the fatal shooting of Minneapolis man Jamar Clark.

While in 2016, at a press conference about Clark's shooting, Lieutenant Kroll called the Black Lives Matter movement a "terrorist organisation".

"I don't see Black Lives Matter as a voice for the black community in Minneapolis," he said.

Don Damond released a statement, shortly after state investigators announced they had finished investigating Ms Damond's death.

"We trust that the Hennepin County Attorney's determination will be based on an astute assessment of the facts," Ms Damond's family said.

Mr Noor has not been detained over the shooting and is yet to speak to authorities about what happened that night.

Mr Freeman is expected to decide on charges before the end of the year.