The US police officers who shot dead an Australian woman who had called 911 for help in Minneapolis did not have their body cameras turned on.
Minnesota's Public Safety Department said a woman was shot in Minneapolis after two officers responded to a callout about a possible assault on Saturday at 11.30pm local time.
Her stepson Zach Damond said she called police after hearing a noise near her house.
"The officers' body cameras were not turned on at the time and the squad camera did not capture the incident," the Bureau of Criminal Apprehension said in a statement.
"Investigators are attempting to determine whether any video of the incident exists."
Mr Damond said the woman, reportedly an Australian in her 40s, 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, she probably thought something bad was happening and then next thing I know they take my best friend's life."
Minneapolis mayor Betsy Hodges said she intended to find out why the officers' body cameras were not turned on.
"As mayor of our city, a wife, and a grandmother, I am heartsick and deeply disturbed by what occurred last night," she posted on Facebook.
© AAP 2017 Photo: Peter Byrne/PA Wire