Before Justine Damond's killer was jailed, her fiancé read a letter to the court.

With AAP.

“Good people sometimes do bad things,” Judge Kathryn Quantance told Mohamed Noor as he stood before her in a U.S. court on Friday, being sentenced for the death of Justine Ruszczyk Damond.

The 40-year-old Australian-born woman was fatally shot by the former police officer on July 15, 2017, after calling 911 to report a possible sexual assault taking place in the alley behind her Minneapolis home. Noor told the court he mistook her as a ‘threat’ and opened fire.

Noor was convicted by a jury of Ruszczyk Damond’s third-degree murder and second-degree manslaughter in April. On Friday, he was handed a 12.5-year prison term.

Ruszczyk Damond’s partner, Don Damond, who was set to marry his “soul mate” in a romantic ceremony in Hawaii just weeks after the tragedy, addressed the court in tears.

It was in the form of a letter he wrote to Ruszczyk Damond.

Damond’s heart-wrenching words included how they were planning to have a baby.

“I miss you every day – every moment,” Damond said.

He explained that following his fiancée’s death he broke down in a dress shop upon seeing the wedding dress she was going to wear.

Ruszczyk Damond’s Australian family members were not in court but their impact statements were read.

Her father requested the maximum sentence and described how “Justine’s death has left me incomplete”.

The murder count carried a maximum 25 years' prison and the manslaughter charge 10 years. Judge Quantance's 12.5 year term matched the guideline sentence and the length proposed by prosecutors.

Noor, who admitted he took the life of "a perfect person", said he had wanted to meet with Damond's family members but was prevented from doing so.

"I've thought and prayed about this for two years, since the time I took the life of Justine Ruszczyk," Noor said before sentencing, according to CNN. "I've also been thinking about all the other lives that have been changed and continue to be changed after this event. None of the families will ever be the same again."

He shared that he hopes to write the family a letter from jail.

"I have wanted to sit with Mr Damond and tell him about what happened and to extend my condolences to him for the last two years as well as to Ms Ruszczyk's other families," Noor said in a voice trembling with emotion.

"The process of the courts and the lawyers (are) so cruel in the way it makes us behave to each other.

"The system is de-humanising."

The judge rejected calls by Noor's lawyers for him to serve an unusual sentence of one week in a low-security jail workhouse on the date of Ruszczyk Damond's death and her birthday during the duration of his parole.

"The act may have been based on a miscalculation, but it was an intentional act," the judge told Noor.

Ruszczyk Damond graduated with a veterinary degree from the University of Sydney, but switched careers to become a life coach, met Damond at a retreat, fell in love, took his surname before their wedding and she moved to Minneapolis. It was her desire to help people that led to her murder.

On July 15 2017, Ms Ruszczyk Damond was home alone in Minneapolis just before midnight,  when she heard a woman screaming in an alley behind her house.

She called 911.

When Ms Ruszczyk Damond approached Noor's police vehicle in the alley he shot across his partner and out the driver's side window, hitting the Australian who was dressed in pyjama pants and a pink t-shirt adorned with a mother and baby koalas.

Noor claimed he was startled.

"The moment I walked around and saw Miss Ruszczyk dying on the ground, I felt horror," Noor said.

Ms Ruszczyk Damond's family filed a $US50 million ($A71 million) civil lawsuit against Minneapolis, and the city agreed to pay $US20 million.

Members of Minneapolis' large Somali expat community protested the sentence outside court, claiming Noor was treated differently to white officers who shot minority members of the public.

Noor's supporters held placards including "Black Muslim Immigrant Guilty" and "Noor: Victim of Identity Politics."

Noor's lawyers Thomas Plunkett and Peter Wold indicated they would appeal.

"We are not done fighting for Mohamed Noor," the lawyers said.