A former US police officer has been jailed over the death of an unarmed Australian woman who had been trying to report a crime when he shot her dead.

Mohamed Noor, 33, was convicted in April of second-degree manslaughter and third-degree murder in the 2017 death of Justine Ruszczyk Damond, 40. Noor was responding to her report of a possible sexual assault in an alley in Minneapolis, Minnesota. On Friday, Judge Kathryn Quaintance sentenced him to 12 years and six months behind bars.

"The act may have been based on a miscalculation, but it was an intentional act," Ms Quaintance said. "Good people sometimes do bad things."

At sentencing, Noor spoke about the incident for the first time and told the judge of his horror over learning he had shot an innocent woman.

"That mistake is my hardship to bear," Noor said as his voice broke.

"Seeing her there, I knew in an instant I was wrong.

"The depth of my error has only increased from that moment on. Working to save her life and watching her slip away is a feeling I can't explain. … It leaves me sad, it leaves me numb, and feeling incredibly lonely. But none of that, none of those words capture what it truly feels like."

Noor shot and killed Ms Damond, when she approached his police vehicle in an alley behind her south Minneapolis home on July 15, 2017.

Ms Damond, formerly of Sydney, had called police to report a possible sexual assault after hearing a woman scream behind her house.

But when an unarmed Ms Damond — dressed in a pink T-shirt with koalas on it, pyjama pants, carrying a glittery gold iPhone — walked towards the patrol car barefoot and to meet police, Noor shot her in the abdomen at point blank range.

The court previously heard that within one minute and 19 seconds of making the emergency call, Ms Damond was cradling a gunshot wound to her abdomen and saying, "I'm dying".

Ms Damond's fiance Don Damond today said his "heart aches every day" when he sees where she died. "In my mind I begged you to turn around," he said.

In a statement read in court, Ms Damond's father John Ruszczyk today asked for Noor to receive the maximum sentence. He said his daughter's death left him incomplete, "as if I have lost a limb or a leg".

Noor previously testified he fired his weapon after he heard a bang on his squad car, saw his partner was scared, then saw Ms Damond at his partner's window, raising her arm. Noor told the court he feared the pair was being targeted in an ambush and "had to make a split-second decision".

Noor said his partner, Officer Matthew Harrity, shouted "Oh Jesus!" and fumbled with his gun in its holster before "he turned to me with fear in his eyes".

Noor and Mr Harrity testified Ms Damond startled them before he shot her through the car window.

Lawyers for Noor, who was fired after being charged in the case and has never talked to investigators about what happened, argue that he used reasonable force to defend himself and his partner from a perceived threat.

Prosecutors claimed Noor acted unreasonably and the shooting wasn't justified.

In her closing arguments this week, prosecutor Amy Sweasy said "this case has tragedy compounded on top of tragedy".

"(Ms Ruszczyk) is gone because she was tragically and violently gunned down by a police officer she called for help," she said.

"He (Noor) knew exactly what he was doing.

"He pointed, he aimed and he killed her."

Ms Damond was living in the US with her American fiance, who she was planning to marry just weeks later when she died.

Mr Damond was in Las Vegas when he got a call from investigators saying Ms Damond was dead, he told the court during his testimony. He said he learned from a second call that she had been shot by an officer.

Mr Damond said calling his fiance's family in Australia to tell them of her death was the "worst phone call" he's ever had to make.

Mr Damond attended the trial every day along with Ms Damond's parents and family who flew in from Australia. The family of the 33 year old Noor, who was sacked after he was charged, also attended the trial.