Justine Damond, 40, from Sydney was killed by police in south Minneapolis on Saturday night.
Minneapolis mayor Betsy Hodges said the incident has made her “heartsick”.
Ms Damond, previously known as Justine Ruszczyk, died following an officer-involved shooting, according to Minneapolis police.
The shooting occurred on the 5100 block of Washburn Avenue South in the city’s Fulton neighbourhood.
The incident is the subject of an investigation but authorities have said the officers who responded to the 911 call did not have their body cameras turned on.
The dead woman’s partner was Don Damond, vice president and manager of Little Six Casino in Minnesota.
His son Zach Damond said Ms Damond “heard a noise in the alley and called the police”.
“She was out on 51st Street and she was shot,” Zach said.
Mr Damond said the woman was “passionate” and his “best friend”.
“Basically my mum was shot for reasons I don’t know,” Mr Damond said in a video posted on Facebook on Monday morning (AEST).
“I just know she heard a sound in the alley so then she called the police and the cops showed up and she was a very passionate woman.