Justine Damond-Ruszczyk’s fiance has given heart-wrenching testimony in a US court about his confusion and shock when a police officer called to say the love of his life had been shot dead.

Don Damond, a US casino executive, wept on the witness stand in Minneapolis on Tuesday as he told how he was in Las Vegas on business the night of July 15, 2017.

Ms Damond, an Australian life coach, called him at 11.37pm from their Minneapolis home, worried a woman was making loud “sex sounds” near an alley behind their house and possibly was being raped.

Mr Damond said he asked her to call police.

The last words she said to him were, “OK, the police are here”.

Mr Damond said he repeatedly tried to call and text her but received no answer and presumed she was fine and gone to bed.

A few hours later, a Minneapolis police officer called.

“He said ‘There has been a shooting and we believe Justine is deceased because of that shooting’,” Mr Damond told packed Hennepin County courtroom.

Mr Damond said he did not believe what the officer was saying and told him: “You have to tell me more”.

Justine Ruszczyk Damond was shot by police after reporting a suspected crime behind her house. Photo: AAP

The officer did not say Minneapolis police officer Mohamed Noor had shot Ms Damond as she approached their patrol car.

Mr Noor, 33, has been charged with second-degree murder, third-degree murder and manslaughter.

Mr Damond said after receiving the call he went to Las Vegas airport to try to fly back to Minneapolis.

While waiting there early on July 16, he took a call on his mobile from a special agent from Minnesota’s Bureau of Criminal Apprehension, who told him a police officer had shot Ms Damond.

“I was in shock,” Mr Damond said.

“I was shaking.

“I said, ‘Please treat her body with dignity’.”

Earlier on Tuesday, Mr Noor’s lawyer, Peter Wold, told the jury in his opening statement that the police officer feared he was the victim of an ambush when Ms Damond suddenly came up to their patrol car in the dark alley.

The shooting, Mr Wold said, “was a perfect storm with tragic circumstances”.

Ms Damond approached the officers’ car after they could not find the woman who Ms Damond feared was being raped.

“It was a classic ambush scenario set-up,” Mr Wold, noting other police incidents in the US, said.

Mr Wold said Ms Damond thumped the police car and Mr Noor’s startled partner, Officer Matthew Harrity, who was driving, said “Oh Jesus” and grabbed his gun.

Mr Noor, in the front passenger seat, shot past Officer Harrity and out the driver’s side window, fatally striking Ms Damond in the stomach.

“Noor shoots once to protect his partner and himself,” Mr Wold said.

“It was a perfect storm with tragic circumstances.”

Mr Wold told the jury Ms Damond’s Australian background added to the perfect storm.

“She came from Australia, where gun violence was virtually non-existent,” he said.

Mr Noor was fired from the police force last year when charged.

Prosecutor Patrick Lofton, in his opening address, said there was no evidence Ms Damond touched the car.

The trial is expected to last three weeks.

Ms Damond’s father, John, and step mother Maryan Heffernan, sat in the front row of the courtroom.

-AAP