The Mayor of Minneapolis has voiced her frustration at not being able to force the police officer responsible for the fatal shooting of Australian woman Justine Damond to be interviewed by investigators.

Key points: It "would be good common sense to investigate" whether sound of fireworks going off startled the officers, source reveals

It "would be good common sense to investigate" whether sound of fireworks going off startled the officers, source reveals Reference to fireworks heard during radio conversations between officers, police dispatchers

Reference to fireworks heard during radio conversations between officers, police dispatchers Mohamed Noor declined to be interviewed by investigators, the update says

Ms Damond, 40, was shot and killed as officers responded to her 911 call about a possible sexual assault in the alley behind her house in Minneapolis on Saturday night (local time).

Minnesota's Bureau of Criminal Apprehension (BCA) said its agents have interviewed the officer who was driving the car, Matthew Harrity, but his passenger and the officer who shot Ms Damond, Mohamed Noor, has declined to be interviewed.

The BCA said his attorney did not indicate when, or if, Mr Noor would be interviewed, adding that it could not force him to be interviewed.

Mohamed Noor has declined to be interviewed by investigators. ( AP: City of Minneapolis )

Mayor Betsy Hodges made an emotional plea at a media conference on Wednesday morning, saying she wished Mr Noor would make a statement.

"We can't compel him by law," she said.

"I wish that he would because he has a story to tell that no-one else can tell.

"I share the frustration of the community at not knowing things we desperately wish we knew."

She has also taken to social media in an effort to "keep the lines of communication open" about the investigation.

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Investigators have said they also want to talk to a cyclist who stopped and watched as officers gave medical aid to Ms Damond.

BCA said it was looking for the man, who is white and 18 to 25-years-old, for help as a possible witness and asked that he and any other possible witnesses contact the agency.

But Teresa Nelson from the American Civil Liberties Union of Minnesota raised concerns the investigation would not be as "vigorous" as needed.

She told 7.30 the BCA was "barely at arm's length" from local police.

"They work with local police on a lot of different things and they need the cooperation of local police to do what they do," Ms Nelson said.

"So they're very closely connected and we would like to see something much more independent."

Ms Hodges also called for any witnesses to come forward.

The attorney for the city of Minneapolis, Susan Segal, said the transcript of the 911 call made by Ms Damond would be released soon.

"I believe it is being transcribed perhaps as we speak and after that is provided to the family, that will be made publicly available and available to the media," she said.

Sounds heard at scene described as 'aerial fireworks'

Mr Harrity has told investigators he was startled by a loud sound near the squad vehicle right before Ms Damond approached the car on his side.

He said Mr Noor shot Ms Damond through the open window, hitting her in the abdomen.

A source with knowledge of Minneapolis law enforcement, who asked not to be identified, said it "would be good common sense to investigate" whether the sound of fireworks going off in the area might have startled Mr Noor into shooting the Australian dead.

The reference to fireworks is heard during the police radio conversations between Mr Noor, Mr Harrity, the police dispatcher coordinating the emergency call and other officers rushing to scene.

At one point during the police radio conversations, the dispatcher asks for a precinct sergeant to acknowledge a report of "two shots heard from the east".

"We heard those sounds from the station," an officer responds.

"Those are probably aerial fireworks."

Mr Harrity and Mr Noor are on paid administrative leave.

Mr Harrity has been with Minneapolis police for one year, and Mr Noor has been with the department for nearly two.

Mr Noor already had two other complaints levelled at him.

Turnbull condemns 'shocking killing'

Sorry, this video has expired PM demands answers over 'shocking killing' of Australian yoga teacher

On Wednesday morning, Prime Minister Malcolm Turnbull said the Federal Government was seeking answers about the "inexplicable" shooting of Ms Damond.

"It is a shocking killing, it is inexplicable," he said.

"We are demanding answers on behalf of her family and our hearts go out to her family and all of her friends and loved ones."

Ms Damond's fiance, businessman Don Damond, has also called for justice for the vet and yoga teacher, who had lived in the US since 2015.

Justine Damond was fatally shot by US police on Saturday night. ( Linkedin: Justine Ruszczyk )

On Tuesday, her father John Ruszczyk said there was an "ugly truth" about the incident.

Family and friends of Ms Damond gathered on a Sydney beach on Wednesday morning to pay silent tribute to the Australian.

Dozens carried candles in the early morning light on Freshwater Beach and each mourner tossed a single pink blossom into the Pacific Ocean.

Pink was the 40-year-old meditation teacher's favourite colour. Almost 300 people gathered for the memorial.

"We're here to come together as a community around our beautiful Justine to honour her life, share our love and mourn her death," the family said in a statement.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 23 seconds 23 s Justine Damond's family and friends held a silent vigil for the 40-year-old. (Photo: Johanna Nicholson)

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