The former Minneapolis police officer who shot dead Australian Justine Damond last year is set to plead not guilty.

Ms Damond suffered the fatal gunshot wound from Mohamed Noor on July 15 after calling police to report a possible sexual assault near her South Minneapolis home.

It has this morning now emerged Noor will plead not guilty on the basis he was acting in self-defence and using reasonable force.

The Australian‘s US correspondent Cameron Stewart broke the news on 3AW Breakfast with Ross and John this morning.

He said a conviction would now be difficult.

“Now of course that does sound prima facie fairly unbelievable that he would do that (plead not guilty),” Houston said.

“But in fact it is going to be a very hard for the prosecutors to win because no policeman in Minneapolis nor the state of Minnesota has ever been prosecuted for fatally shooting someone.”

Click PLAY to hear more from Cameron Houston (Justine Damond news from 4:41)