MINNEAPOLIS -- The fiance of a yoga instructor who was fatally shot by Minneapolis police over the weekend gave an emotional statement to the media Monday, saying, "our hearts are broken."

Details about what led to the shooting are beginning to emerge, with authorities saying that officers were responding to a 911 call about a possible assault when the woman was killed.

A law enforcement source said it's unclear why the officer discharged his weapon, CBS News' Pat Milton reports. The officer apparently had his gun drawn when the two officers arrived at the scene in the cruiser.

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The driver's side window was open and the bullet traveled past the officer seated in the driver's seat and through the open window. It hit a woman standing at the window, but it's unclear if the woman was talking to the officers at the time or had just approached the window, Milton adds.

Minneapolis authorities have not released the woman's name. The Star Tribune identified her as Justine Damond, 40, from Sydney, Australia. Friends and neighbors also identified her as Justine Damond, CBS Minnesota reports. Milton reports that the incident occurred in an affluent neighborhood.

The Star Tribune reported that she was engaged to be married and had already taken her fiance's last name. Her maiden name was Justine Ruszczyk.

Citing three people with knowledge of the shooting it did not name, the newspaper said Damond had been the one to call 911 about a possible assault in the alley behind her house. On Monday, her fiance Don Damond said she had been reporting "what she believed was an active sexual assault occurring nearby."

"Sadly, her family and I have been provided with almost no additional information from law enforcement regarding what happened after police arrived," Don Damond told reporters. "We've lost the dearest of people and we are desperate for information. Piecing together Justine's last moments before the homicide would be a small comfort as we grieve this tragedy."

He said Justine was "a teacher to so many" who "touched so many people with her loving and generous heart."

"She was so kind, and so darn funny, she made all of us laugh with her great wit and her humor," he said. "It's difficult to fathom how to go forward without her in my life."

The woman's family members released a statement Monday through Australia's Department of Foreign Affairs and Trade, saying they "are trying to come to terms with this tragedy and to understand why this has happened."

The BCA said Monday that no weapons were found at the scene.

The officer who fired his weapon has been identified as Mohamed Noor, who is a Somali-American, a law enforcement source confirmed to CBS News. His attorney, Tom Plunkett, released a statement to the station saying: "We take this seriously with great compassion for all persons who are being touched by this."

According to a city newsletter, Noor joined the police department in March 2015.

According to several eyewitnesses, Damond, in her pajamas, approached the responding police car and was standing at the driver's window when Noor, who was in the passenger seat, shot her through the driver's side door.

Police referred questions to the BCA. A spokeswoman for the agency did not return messages seeking to confirm that account. A Monday statement from the BCA said more information would be provided once the officers were interviewed.

Neighbor Joan Hargrave called the killing "an execution" and said there was no reason for a well-trained officer to see Damond as a threat.

"This is a tragedy - that someone who's asking for help would call the police and get shot by the police," Hargrave said.

Officials said the officers' body cameras were not turned on and that a squad car camera did not capture the shooting. Investigators were still trying to determine whether other video exists.

It's not clear why the officers' body cameras were not turned on. The department's policy allows for a range of situations in which officers are supposed to do so, including "any contact involving criminal activity" and before use of force. If a body camera is not turned on before use of force, it's supposed to be turned on as soon as it's safe to do so.

Once the investigation is complete, it would be up to Hennepin County Attorney Mike Freeman to decide whether to charge the officer.

Freeman would not comment on the broader case Monday, but said both officers likely should have turned on their body cameras as they were approached by Damond in an alley.

Police Chief Janee Harteau called the killing a "tragic death" and said she understands why the community has questions. "I've asked for the investigation to be expedited to provide transparency and to answer as many questions as quickly as we can," she said.

The Fulton neighborhood where the shooting happened is a mix of middle- and upper-middle-class homes about a half-mile from city lakes that are a popular destination for residents and tourists.

Some 50 friends and neighbors gathered in a semicircle Sunday near the shooting site, with many more looking on from the sidewalk and street. Chalk hearts containing the names of some people who were victims of police violence were drawn on the driveway.

By Monday, flowers had also been left at the scene, along with a handwritten sign that asked, "Why did you shoot and kill our neighbor?"

Damond's death is yet another high-profile police shooting in the Twin Cities area in recent years. Last year, 32-year-old Philando Castile was killed by an officer during a traffic stop in a nearby suburb after he told the officer he was armed. And in November 2015, a Minneapolis police officer shot and killed Jamar Clark during a struggle in which the officer said Clark grabbed his partner's weapon.

Damond's business website indicates that she relocated to Minneapolis and worked as a yoga instructor, meditation teacher and personal health and life coach.

Originally trained as a veterinarian, Damond indicted on the site that she was "most passionate about supporting individuals and organizations to discover the power and potential within their own brains and hearts."

Damond's mother was Australian, and she spent her formative years there, but also spent some of her early childhood in the Buffalo, New York, area, said Peter Suffoletto, a cousin of Damond's father. Suffoletto said Damond frequently returned to New York state, and stayed with Suffoletto and his wife, Elaine, in Hamburg, New York, as recently as April.

"She was the sweetest soul that I've ever met," Elaine Suffoletto said.

Peter Suffoletto added: "She was just a loving free spirit... We're devastated, beyond devastated."

Don Damond's son Zach Damond, 22, said Justine Damond was engaged to marry his father next month.

"Basically, my mom's dead because a police officer shot her for reasons I don't know," Zach Damond said. "I demand answers."