Police in Minnesota were startled by a loud sound prior to fatally shooting an unarmed Australian woman who had called them to report a possible assault, US investigators revealed Tuesday.

The state agency probing the killing of Justine Damond, also known by her maiden name Justine Ruszczyk, interviewed one of the two officers who responded to her emergency call on Saturday night in Minneapolis.

It was the first time since the incident that authorities offered more information about the circumstances, as community leaders and Damond's family complained they had few details over a killing that reverberated in her native Australia.

Damond had called Minneapolis police Saturday around 11:30 pm to report a possible assault occurring near her home. Two officers responded with their police car's emergency lights off.

Officer Matthew Harrity told investigators Tuesday that he had been "startled by a loud sound" near the squad car just before Damond approached, the Minnesota Bureau of Criminal Apprehension (BCA) said in a statement.

His partner, Officer Mohamed Noor, was in the passenger seat.

"Harrity indicated that Officer Noor discharged his weapon, striking Ruszczyk through the open driver's side window," the agency said.

The BCA did not identify the startling sound, but an unidentified officer recorded on a police radio conversation published by the website Minnesota PoliceClips, speculated it may have been fireworks that sounded like gun shots.

After the shooting, the officers provided medical aid until paramedics arrived, but Damond died at the scene of a gunshot wound to the abdomen, authorities said.

The officers' body-worn cameras were not on during the incident, and investigators appealed for witnesses to come forward.

Meanwhile, Minneapolis officials pressed for patience, saying the state investigation took precedence and city authorities therefore had little information of their own to share.

"We don't have all the answers," Minneapolis Mayor Betsy Hodges said at a Tuesday night news conference.

"But, the information the BCA shared this evening gets us closer to having answers, closer to seeing justice done," she said.

- Australia mourns -

Damond, a 40-year-old meditation instructor and life coach, was an Australian national who had moved to the US to marry her fiance Don Damond -- who on Monday had criticized a lack of information from investigators.

Her death reverberated around the world, from a makeshift memorial at the Lake Harriet Spiritual Community center where Damond worked, to her native Australia.

Hundreds of family and friends gathered for an emotional vigil at Sydney's Freshwater beach at daybreak on Wednesday, standing in silence and holding candles before casting pink flowers into the water.

In an interview with Australia's Channel Nine, Prime Minister Malcolm Turnbull on Wednesday expressed shock.

"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."

A day earlier, Damond's father John Ruszczyk addressed Australian media at a news conference, calling for justice.

"Justine was a beacon to all of us. We only ask that the light of justice shine down on the circumstances of her death," he said.

- Officer 'a caring person' -

Noor, who has been with the Minneapolis police force for 21 months, declined investigators' requests for an interview, the BCA said Tuesday.

"We cannot compel Officer Noor to make a statement," Mayor Hodges said, "I wish that he would... because he has a story to tell that no one else can tell."

In a statement, Noor's attorney Tom Plunkett called the officer "a caring person," who "empathizes with the loss others are experiencing." But Plunkett said ongoing investigations prevented the officer from saying any more.

There are three investigations, one conducted by the BCA which takes precedence, a police department use of force review, and a civilian oversight civil rights probe that has not yet begun.

Damond's case was the latest high-profile police shooting. Most others involved white police officers and African American victims. In this case, Noor is Somali American, while Damond was white.

"Justine's death shows no one should assume 'officer-involved shootings' only happen in a certain part of town or to certain kinds of people," Congressman Keith Ellison, who represents Damond's district in the US House of Representatives, said in a statement.

source: AFP