A Minnesota prosecutor who criticised agents investigating the death of an Australian woman fatally shot by an officer has apologised for his comments.

Key points: Prosecutor Mike Freeman says he didn't know comments being recorded

Prosecutor Mike Freeman says he didn't know comments being recorded He says comments ill advised

He says comments ill advised Freeman to share more information next week on whether to charge officer

Hennepin County attorney Mike Freeman publicly apologised on Monday to the state Bureau of Criminal Apprehension.

Last week, Mr Freeman told a group of activists that he doesn't have enough evidence yet to charge the Minneapolis police officer who killed Justine Damond last July, saying investigators, "haven't done their job".

Mr Freeman said he believed it was his responsibility to talk to constituents, but he was wrong to discuss the agency's work.

He also said he did not know he was being recorded, but his comments were ill advised.

Mr Freeman was captured on video expressing his frustration at a Minneapolis Regional Labor Federation holiday reception on Wednesday night, after he was asked about a charging decision.

Union member Sam Sanchez recorded the conversation and posted it on Facebook.

In the video, Mr Freeman said he did not have enough evidence yet to decide whether to charge officer Mohamed Noor, who has declined to speak with investigators.

"I've got to have the evidence. And I don't have it yet. And let me just say, it's not my fault," Mr Freeman said.

"So if it isn't my fault, who didn't do their jobs? Investigators. And they don't work for me. And they haven't done their job."

Mr Noor shot Ms Damond in the alley behind her home in July.

Mohamed Noor shot Justine Damond as he sat in the passenger seat of a Minneapolis police car ( AP: City of Minneapolis )

Ms Damond had called 911 to report a possible sexual assault.

As she approached the squad car, Mr Noor fired from the passenger seat, across his partner and through the driver's window.

Ms Damond's death sparked protests and led to a police department shake-up, including the resignation of chief Janee Harteau.

Mr Freeman said he would share information next week on the status of his decision on whether to charge Mr Noor.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 2 minutes 17 seconds 2 m 17 s Why was Justine Damond Ruszczyk shot?

AP