Mohamed Noor refused to talk to investigators after the July 2017 shooting of Justine Ruszczyk Damond , a dual citizen of the US and Australia, making his testimony his first public statements since her death.

Damond had called 911 minutes earlier to report a possible sexual assault behind her home, and was shot as she approached Noor's squad car as he and his partner slowly rolled down her alley looking for evidence of a woman in distress.

Noor testified that he fired to stop what he thought was a threat to him and his partner, Matthew Harrity, after he heard a loud bang on the driver's side of the squad car.

Noor said he saw fear in Harrity's eyes and saw that Harrity was trying to pull his gun but was having difficulty.

He described putting his left arm over Harrity's chest, and seeing a woman in a pink shirt with blond hair outside Harrity's driver's side window raising her right arm.

"I fired one shot," Noor said. "My intent was to stop the threat."

When he realised he had shot an innocent woman, Noor said, "I felt like my whole world came crashing down."

"I couldn't breathe," Noor said. "I felt great pain."

Prosecutor Amy Sweasy attacked Noor in cross-examination, noting that Noor didn't see Damond's hands or a weapon.

"You meant to shoot the woman to stop the threat?" she asked. "You knew you were shooting a person?"

"Yes ma'am," he answered.

Noor was fired from the force soon after being charged. His lawyers have said he was spooked by a noise on his squad car right before the shooting and feared an ambush.

The death of Damond, a 40-year-old life coach who was engaged to be married a month after her death, sparked anger and disbelief in both the US and Australia, cost the city's police chief her job and contributed to the mayor's electoral defeat a few months later.

Prosecutors have questioned the supposed noise, presumably from Damond slapping the car as she approached, by noting that investigators didn't find forensic evidence of Damond's fingerprints on the car.

They also questioned the timing of Harrity's first mention of the thump - not the night of the shooting, but a few days later, as he was being interviewed by state investigators.

Neither officer had their body cameras running when Damond was shot, something Harrity blamed on what he called a vague policy that didn't require it.

The department toughened the policy after Damond's death to require that the cameras be turned on when responding to a call.

Damond was white. Noor, 33, is a Somali American whose hiring two years before the shooting was celebrated by Minneapolis leaders as a sign of a diversifying police force in a city with a large population of Somali immigrants.

Noor testified earlier on TThursday about immigrating from Somalia to the US, where he became a citizen in 1999. He lived first in Chicago, then moved to Minneapolis, where he said he fell in love with the city.

He said he became a police officer because he "wanted to serve".

Australian Associated Press